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Old 12-09-2021, 09:30 AM   #1
cplvan
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Default P0131 code with hesitation when accelerating and poor gas mileage

Hi, I was driving to work the other day and I started getting a hesitation when I would press on the gas but it would go away when I gave it more throttle. I also noticed that my gas mpg was about half what in normally does (I guess it was running very rich?). I took it to AutoZone to look at the codes and there were three codes. P0131 O2 Circuit Low Voltage (bank 1 sensor 1), p0300 engine misfire detected, p0440 evaporative emission (EVAP) system.

MY car is 2001 saturn SL w/ 1.9 SOHC

any suggestions on what to do?
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Old 12-09-2021, 10:17 AM   #2
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Default Re: P0131 code with hesitation when accelerating and poor gas mileage

Here is OldNuc advice on the O2 sensor:
http://www.saturnfans.com/forums/sho...25&postcount=2

I'd go after the P0300 first. Have you ever changed plugs and wires? This is a basic tuneup thing which can cause a misfire. The P0300 is probably the major problem.

Plugs:
http://www.saturnfans.com/forums/sho...37&postcount=8

Evap won't cause power or fuel economy problems.

Somebody will be along shortly to mandate a compression test. While that's not a bad thing I think the amount of catastrophic failures is low.
...
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Old 12-09-2021, 10:29 AM   #3
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Default Re: P0131 code with hesitation when accelerating and poor gas mileage

There's a lot going on there but I'll take a stab at what might be the root cause problem which waterfalls into other issues you are experiencing.

What does your temp gauge read when at full operating temperature? If it is close to 1/4 then you likely need to do one or all of the following. Replace your ETCS sensor, replace the ETCS sensor wire harness connector and replace the thermostat.

The ETCS sensor installed in 2001 models is resin tipped and it is prone to cracking and fouling the connector. This sends an incorrect reading to the ECU and the ECU thinks your engine is running cool so it increases fuel. This results in poor fuel mileage and increased carbonization in the engine and exhaust components. One of those is your O2 sensor on the exhaust manifold hence the P0131. The other component is the Air Injection System connected to your exhaust manifold which relates to the P0440.

Check your ETCS sensor or just replace it with a brass tipped version. If it is cracked then also inspect or just replace your connector making sure to solder and shrink tube the connections to the wire harness. Crimp connectors are a common point of failure in this circuit.

After this, if your gauge temperature does not increase when at operating temperature then replace your thermostat as it has likely failed open and your engine is actually running cool (and the ECU is increasing fuel and you are getting carbonization).

You will likely need to deal with the carbonization problem too by replacing your O2 sensor and removing the carbonization in the exhaust manifold passages including the tube that goes into the air injection system and the pre-cat. Sometimes you can get away with just cleaning out the tube going to the air injection system off the manifold.

It wouldn't hurt to clean your throttle body and EGR too. Plugs and wires if close to service life as Waiex191 suggests is also a good measure.
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Last edited by trottida; 12-09-2021 at 10:38 AM.
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Old 12-09-2021, 12:35 PM   #4
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Default Re: P0131 code with hesitation when accelerating and poor gas mileage

Quote:
Originally Posted by Waiex191 View Post
Here is OldNuc advice on the O2 sensor:
http://www.saturnfans.com/forums/sho...25&postcount=2

I'd go after the P0300 first. Have you ever changed plugs and wires? This is a basic tuneup thing which can cause a misfire. The P0300 is probably the major problem.

Plugs:
http://www.saturnfans.com/forums/sho...37&postcount=8

Evap won't cause power or fuel economy problems.

Somebody will be along shortly to mandate a compression test. While that's not a bad thing I think the amount of catastrophic failures is low.
I replaced the plugs and wires a few months ago. not sure what brand. SO would you suggest that I replace the spark plugs? or should i replace the o2 sensor? i have a hard time beliveing changing my spark plugs would create or fix the issue.
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Old 12-09-2021, 12:52 PM   #5
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Default Re: P0131 code with hesitation when accelerating and poor gas mileage

Quote:
Originally Posted by trottida View Post
There's a lot going on there but I'll take a stab at what might be the root cause problem which waterfalls into other issues you are experiencing.

What does your temp gauge read when at full operating temperature? If it is close to 1/4 then you likely need to do one or all of the following. Replace your ETCS sensor, replace the ETCS sensor wire harness connector and replace the thermostat.

The ETCS sensor installed in 2001 models is resin tipped and it is prone to cracking and fouling the connector. This sends an incorrect reading to the ECU and the ECU thinks your engine is running cool so it increases fuel. This results in poor fuel mileage and increased carbonization in the engine and exhaust components. One of those is your O2 sensor on the exhaust manifold hence the P0131. The other component is the Air Injection System connected to your exhaust manifold which relates to the P0440.

Check your ETCS sensor or just replace it with a brass tipped version. If it is cracked then also inspect or just replace your connector making sure to solder and shrink tube the connections to the wire harness. Crimp connectors are a common point of failure in this circuit.

After this, if your gauge temperature does not increase when at operating temperature then replace your thermostat as it has likely failed open and your engine is actually running cool (and the ECU is increasing fuel and you are getting carbonization).

You will likely need to deal with the carbonization problem too by replacing your O2 sensor and removing the carbonization in the exhaust manifold passages including the tube that goes into the air injection system and the pre-cat. Sometimes you can get away with just cleaning out the tube going to the air injection system off the manifold.

It wouldn't hurt to clean your throttle body and EGR too. Plugs and wires if close to service life as Waiex191 suggests is also a good measure.
my temp gage is a little over 1/4but okay ill check out the ETCS sensor. where is it located? what should be my first step into checking this sensor?

also i dont think i need to replace my thermostat because if it failed to open my engine would be running to hot not to cold. right? because when the the thermostat is stuck closed no coolant is getting into the engine to cool it down,
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Old 12-09-2021, 02:02 PM   #6
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Default Re: P0131 code with hesitation when accelerating and poor gas mileage

Both the ECTS and thermostat have higher than average failure rates in the S-Series.

The factory ECTS is made of a resin that cracks when exposed to the chemicals in coolant over 4-5 years, this long after the last S-Series was built I'd expect them all to have a proper brass ECTS now. The air temp sensor and if you have an automatic transmission the trans temp sensor is the same part number as the ECTS yet they virtually never fail in those locations.

The thermostat usually fails in the fully open position, this is the opposite of "fails to open." With it stuck open it allows coolant to flow through the engine at whatever high rate the water pump makes, which results in the engine running colder than it should (195-205f is good, 160-180 is cold, 210-220f is hot).

Cheapest way to tell which is needed is to stick another thermometer in the coolant reservoir to get a 2nd opinion of the coolant temp. Depending on the accuracy of the thermometer I'd expect up to 10f difference. Don't use a standard house thermometer, they top out under 130f while you're expecting a reading 150-200f.

With your car being a '00-'02 and having misfire issue's I'd also look at the engine idle speed. If it's over 800rpm after the coolant temp issue is fixed you likely have a vacuum leak at the intake manifold gasket. Should be simple to diagnose, take a can of brake cleaner or carb cleaner and spray around the intake manifold flange, if engine RPM change's then it's for sure leaking.
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Old 12-09-2021, 03:46 PM   #7
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Default Re: P0131 code with hesitation when accelerating and poor gas mileage

Quote:
Originally Posted by cplvan View Post
my temp gage is a little over 1/4but okay ill check out the ETCS sensor. where is it located? what should be my first step into checking this sensor?

also i dont think i need to replace my thermostat because if it failed to open my engine would be running to hot not to cold. right? because when the the thermostat is stuck closed no coolant is getting into the engine to cool it down,
Classic S Series symptom is a low temp reading. This is about the correct reading for a GEN3 like yours; give or take a needle width.



Below is a photo showing the ECTS location with the battery removed and here is a relevant video >> https://youtu.be/cucm7QGlsYs. I think this is a GEN2 which has a few engine bay differences but the ECTS is in the same location. There is a second photo of the difference between a brass tipped and resin sensor. You want a brass tipped in there.

Pinch the sides of the ECTS connector to remove it and use the appropriate sized socket to remove the sensor. You will loose a bit of coolant and it helps if you raise the left front corner of the car. Inspect the tip for cracks or just replace it. Inspect the pins on the connector to make sure they are clean; no coolant residue or dirt. Here's a link to a relevant video for replacing the connector >>https://youtu.be/mNZq6PuOi5c

The thermostat typically fails open on these allowing coolant to circulate and over cooling the engine. Here's a relevant video for replacement >> https://youtu.be/JEoLFrg8IUI and this one >> https://youtu.be/dVLoeoDU5E8



...
1999 SL2 MT (299,400 km @ 11/2021)
2012 Ford Focus SEL HB MT
2011 Suburban LT

Past Saturns
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1993 SW2 AT (10y)
2001 LW200 MT (3.5y)
1992 SL2 MT (5y)

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Last edited by trottida; 12-09-2021 at 03:56 PM.
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Old 12-09-2021, 08:17 PM   #8
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Default Re: P0131 code with hesitation when accelerating and poor gas mileage

Quote:
Originally Posted by trottida View Post
Classic S Series symptom is a low temp reading. This is about the correct reading for a GEN3 like yours; give or take a needle width.



Below is a photo showing the ECTS location with the battery removed and here is a relevant video >> https://youtu.be/cucm7QGlsYs. I think this is a GEN2 which has a few engine bay differences but the ECTS is in the same location. There is a second photo of the difference between a brass tipped and resin sensor. You want a brass tipped in there.

Pinch the sides of the ECTS connector to remove it and use the appropriate sized socket to remove the sensor. You will loose a bit of coolant and it helps if you raise the left front corner of the car. Inspect the tip for cracks or just replace it. Inspect the pins on the connector to make sure they are clean; no coolant residue or dirt. Here's a link to a relevant video for replacing the connector >>https://youtu.be/mNZq6PuOi5c

The thermostat typically fails open on these allowing coolant to circulate and over cooling the engine. Here's a relevant video for replacement >> https://youtu.be/JEoLFrg8IUI and this one >> https://youtu.be/dVLoeoDU5E8



I replaced the ECTS and the wiring looked fine and no corrosion. The problem is still there. Do you recommend replacing the bank 1 sensor 1 o2 sensor?
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Old 12-09-2021, 08:55 PM   #9
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Default Re: P0131 code with hesitation when accelerating and poor gas mileage

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Originally Posted by cplvan View Post
I replaced the ECTS and the wiring looked fine and no corrosion. The problem is still there. Do you recommend replacing the bank 1 sensor 1 o2 sensor?
Has the temperature increased at full operating temperature? The first step is to remove the root cause and get your operating temperature where it should be. The second step is to resolve the secondary issues caused by the root cause. Let's confirm the issue from step 1 is resolved.
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2011 Suburban LT

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Old 12-10-2021, 09:05 AM   #10
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Default Re: P0131 code with hesitation when accelerating and poor gas mileage

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Originally Posted by trottida View Post
Has the temperature increased at full operating temperature? The first step is to remove the root cause and get your operating temperature where it should be. The second step is to resolve the secondary issues caused by the root cause. Let's confirm the issue from step 1 is resolved.
No, the needle is still just a little bit above 1/4. Do you suggest changing out the thermostat? I feel like that's a decent amount of work for something we don't know is the problem. my needle has always been a little above 1/4 of the way ever since I've owned the car and I never had any problems in the past. thank you for the help
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Old 12-10-2021, 11:24 AM   #11
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Default Re: P0131 code with hesitation when accelerating and poor gas mileage

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Originally Posted by cplvan View Post
No, the needle is still just a little bit above 1/4. Do you suggest changing out the thermostat? I feel like that's a decent amount of work for something we don't know is the problem. my needle has always been a little above 1/4 of the way ever since I've owned the car and I never had any problems in the past. thank you for the help
Yes, change out the thermostat. The recommended thermostat is a Stant 14279 and it reuses the OEM housing. If there is an aftermarket housing currently installed (like MotoRad) the Stant won't fit properly and you'll get an overheat situation. The Stant thermostat has a crack open temp of 188 and fully open temp of 195 like the OEM thermostat. There are other brands that are 185/192 out there as an FYI; I believe they are for warmer climates.

To explain why you haven't had issues before while the coolant temperature is so low; it takes time for the downstream problem of carbonization due to a fuel rich situation to present. It's a waterfall effect which you are just noticing now and it is getting slowly degrading one part at at time.

You can replace your O2 sensor and clean up the exhaust manifold, throttle body and EGR but without resolving the root cause (low temp) you are just going to be wasting parts and labour. Let's get the operating temperature to where it is supposed to be (around 192 degrees Fahrenheit) first then resolve the subsequent issues. Replacing the thermostat will likely resolve you high idle problem and increase your fuel mileage.

This is a pretty common issue for the S Series and well documented all over this forum.
...
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2012 Ford Focus SEL HB MT
2011 Suburban LT

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1993 SW2 AT (10y)
2001 LW200 MT (3.5y)
1992 SL2 MT (5y)

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Last edited by trottida; 12-10-2021 at 11:34 AM.
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Old 12-10-2021, 02:03 PM   #12
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Default Re: P0131 code with hesitation when accelerating and poor gas mileage

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Originally Posted by trottida View Post
Yes, change out the thermostat. The recommended thermostat is a Stant 14279 and it reuses the OEM housing. If there is an aftermarket housing currently installed (like MotoRad) the Stant won't fit properly and you'll get an overheat situation. The Stant thermostat has a crack open temp of 188 and fully open temp of 195 like the OEM thermostat. There are other brands that are 185/192 out there as an FYI; I believe they are for warmer climates.

To explain why you haven't had issues before while the coolant temperature is so low; it takes time for the downstream problem of carbonization due to a fuel rich situation to present. It's a waterfall effect which you are just noticing now and it is getting slowly degrading one part at at time.

You can replace your O2 sensor and clean up the exhaust manifold, throttle body and EGR but without resolving the root cause (low temp) you are just going to be wasting parts and labour. Let's get the operating temperature to where it is supposed to be (around 192 degrees Fahrenheit) first then resolve the subsequent issues. Replacing the thermostat will likely resolve you high idle problem and increase your fuel mileage.

This is a pretty common issue for the S Series and well documented all over this forum.
ok i will replace the thermostat. i dont need to replace the thermostat housing if it looks like its not leaking. right?
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Old 12-10-2021, 02:11 PM   #13
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Default Re: P0131 code with hesitation when accelerating and poor gas mileage

Also, I just replaced my heater core and never bled the coolant to get the air out of the system. do you think if i just bled the coolant this problem would go away? im guessing not but worth the ask
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Old 12-10-2021, 02:28 PM   #14
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Default Re: P0131 code with hesitation when accelerating and poor gas mileage

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Also, I just replaced my heater core and never bled the coolant to get the air out of the system. do you think if i just bled the coolant this problem would go away? im guessing not but worth the ask
No special bleeding required. Run it and top off as required.
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Old 12-10-2021, 02:34 PM   #15
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Default Re: P0131 code with hesitation when accelerating and poor gas mileage

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ok i will replace the thermostat. i dont need to replace the thermostat housing if it looks like its not leaking. right?
The coolant housing is re-usable for sure. You may want to replace the o-ring; I can't recall if it comes with the thermostat; it probably does. Just make sure the housing is compatible. OEM housing works with Stant whereas aftermarket does not.

Quote:
Originally Posted by cplvan View Post
Also, I just replaced my heater core and never bled the coolant to get the air out of the system. do you think if i just bled the coolant this problem would go away? im guessing not but worth the ask
The system is self bleeding by just running it. I don't think it is related.
...
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2012 Ford Focus SEL HB MT
2011 Suburban LT

Past Saturns
2001 SL1 MT (438,500 km 11y)
1993 SW2 AT (10y)
2001 LW200 MT (3.5y)
1992 SL2 MT (5y)

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Old 12-11-2021, 12:33 PM   #16
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Default Re: P0131 code with hesitation when accelerating and poor gas mileage

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Below is a photo showing the ECTS location with the battery removed . . . I think this is a GEN2
Yep, that's my '98. You can see the white shrink-wrap showing the ECTS connector had been changed at that point.

Quote:
I replaced the plugs and wires a few months ago. not sure what brand. . . . i have a hard time beliveing changing my spark plugs would create or fix the issue.
The spark plug brand doesn't matter much, spark plug type does. Fine-wire/single platinum plugs have a reputation for fouling in these engines, causing the P0300 series of misfire codes. Double-platinum or copper-core plugs will be fine. If you are not sure of the type, the auto parts store you got them at will have a record if you have an account there.

If not, they can do the parts lookup and see what their recommended plug is (probably a copper-core plug), and what t they recommend as the next step "up" is (probably a single-platinum plug). IF you got the single-plat, then at least inspect them, and if fouled, definitely replace with copper core.

Does the car run rough at idle?
How many miles on engine?
Has fuel filter ever been replaced?
good spark at all 4 plugs?
There are some good (free) troubleshooting steps here (pulling O2 sensor to check for blocked cat - or precat, since you have a 3rd gen and put a metal heat block to cover plastic parts in front, ICM switching, EGR blocking), worth a read:

http://www.saturnfans.com/forums/sho...d.php?t=184377
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Old 12-13-2021, 04:17 PM   #17
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Default Re: P0131 code with hesitation when accelerating and poor gas mileage

Quote:
Originally Posted by alordofchaos View Post
Yep, that's my '98. You can see the white shrink-wrap showing the ECTS connector had been changed at that point.

The spark plug brand doesn't matter much, spark plug type does. Fine-wire/single platinum plugs have a reputation for fouling in these engines, causing the P0300 series of misfire codes. Double-platinum or copper-core plugs will be fine. If you are not sure of the type, the auto parts store you got them at will have a record if you have an account there.

If not, they can do the parts lookup and see what their recommended plug is (probably a copper-core plug), and what t they recommend as the next step "up" is (probably a single-platinum plug). IF you got the single-plat, then at least inspect them, and if fouled, definitely replace with copper core.

Does the car run rough at idle?
How many miles on engine?
Has fuel filter ever been replaced?
good spark at all 4 plugs?
There are some good (free) troubleshooting steps here (pulling O2 sensor to check for blocked cat - or precat, since you have a 3rd gen and put a metal heat block to cover plastic parts in front, ICM switching, EGR blocking), worth a read:

http://www.saturnfans.com/forums/sho...d.php?t=184377
okay.
Does the car run rough at idle? no it runs fine at idle
How many miles on engine? about 75,000
Has fuel filter ever been replaced? i dont think so
good spark at all 4 plugs? and yes good spark on all 4 plugs
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Old 12-14-2021, 08:48 AM   #18
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Default Re: P0131 code with hesitation when accelerating and poor gas mileage

Quote:
Originally Posted by trottida View Post
The coolant housing is re-usable for sure. You may want to replace the o-ring; I can't recall if it comes with the thermostat; it probably does. Just make sure the housing is compatible. OEM housing works with Stant whereas aftermarket does not.



The system is self bleeding by just running it. I don't think it is related.
ok so I replaced the thermostat. I also removed the battery and put it back just to clear the codes and reset the computer. Drove it into work today (70 mile trip) and the check engine light never came back on and I'm not getting the hesitation while I'm accelerating. So that's good but I noticed I'm still getting horrible fuel mileage. I'm getting about 15 mpg when I used to be getting 30-35. any ideas? also it looks like the operating temp is back up to normal. I took a picture of the gage. see the picture for reference.
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Old 12-14-2021, 12:41 PM   #19
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Join Date: Oct 2005
Location: North of North of Toronto, Northern Ontario, Canada
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1999 SL2
2001 SL1
Default Re: P0131 code with hesitation when accelerating and poor gas mileage

Quote:
Originally Posted by cplvan View Post
ok so I replaced the thermostat. I also removed the battery and put it back just to clear the codes and reset the computer. Drove it into work today (70 mile trip) and the check engine light never came back on and I'm not getting the hesitation while I'm accelerating. So that's good but I noticed I'm still getting horrible fuel mileage. I'm getting about 15 mpg when I used to be getting 30-35. any ideas? also it looks like the operating temp is back up to normal. I took a picture of the gage. see the picture for reference.
It's good that you see a positive change after changing out the thermostat; you know that you've done something right however I'm stumped as to why you are still experiencing poor fuel mileage.

What brand thermostat did you put in there? Do you know for sure the outgoing one was OEM style and the housing is OEM? I ask because your temp reading now seems high for a GEN3. This would happen when you put an OEM thermostat in an aftermarket housing (like MotoRad). It restricts the thermostat from fully opening. I don't think this would affect fuel mileage though. It would cause your cooling fan to run more often then usual.

I assume this picture is showing operating temperature; the temperature when the car is warmed up and lots of air is moving through the radiator. I'm guessing this reading is around 211 degrees Fahrenheit. Do you have a scanner? What temp reading does it show?

Back to the fuel mileage. You'd expect to see an drop in fuel mileage in the colder months; especially if you are pre-heating the car before leaving. I'm not sure what climate you are in. Low tire pressure would also contribute; have you topped them up since the cold weather arrived? What spark plugs did you have installed? You might want to pull them and see what brand/style/product number they are and note the condition of the tip (dry/wet/oily/white-ish/etc...). The wrong spark plug may affect fuel mileage. Does your exhaust smell like gas?

Anybody else have some ideas?
...
1999 SL2 MT (299,400 km @ 11/2021)
2012 Ford Focus SEL HB MT
2011 Suburban LT

Past Saturns
2001 SL1 MT (438,500 km 11y)
1993 SW2 AT (10y)
2001 LW200 MT (3.5y)
1992 SL2 MT (5y)

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Old 12-14-2021, 01:26 PM   #20
trottida
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Join Date: Oct 2005
Location: North of North of Toronto, Northern Ontario, Canada
Posts: 2,992
 

1999 SL2
2001 SL1
Default Re: P0131 code with hesitation when accelerating and poor gas mileage

Check for vacuum leaks....

Quote:
On fuel injected engines, the unaccounted-for air confuses the computer, which will attempt to compensate for the additional airflow by increasing relative fuel flow.
It may also result in a p0440 code.
...
1999 SL2 MT (299,400 km @ 11/2021)
2012 Ford Focus SEL HB MT
2011 Suburban LT

Past Saturns
2001 SL1 MT (438,500 km 11y)
1993 SW2 AT (10y)
2001 LW200 MT (3.5y)
1992 SL2 MT (5y)

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