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Old 02-12-2019, 04:03 PM   #1
JF01saturn
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Default Idle questions/ gas mileage

2001 Saturn SW2 DOHC. What should the idle rpm be at temp? With and w/o ac on? Where should the temp gauge be at fulll temp? Mine is just hardly above the 1/4 mark.

I believe I have a TPS issue. When I come out of a shift and push in the clutch the idle hangs for a bit at about 1300-1500 then it comes down to about 900-1000. Also the idle has ďstuckĒ before at about 2000 RPMs and doesnít want to come down. Shut it off and restart and it seems okay. So Iím thinking itís TPS. I have one on the way to replace anyways.

Also am getting horrible MPG. 22 with a lot of city driving. I deliver pizzas, great college job. I have new NGK plugs on the way, I checked the throttle body and it was clean and the air filter was clean. Thinking of putting in a new stat as well. I bought the car last week. 90k original miles.

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Old 02-12-2019, 04:46 PM   #2
Silverblu02SL2
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2002 SL2
Default Re: Idle questions/ gas mileage

My 2002 SL2 I acquired a few weeks ago, the last fillup was 20 mpg. probably 50/ 50 city/ hwy with quite a bit of idling trying to diagnose/ fix issues.

Does gasoline have summer / winter fuel? I am new to gasoline vehicles, been all diesels last 30 years. Winter diesel fuel in cold climates have less BTU's due to being diluted with Kerosene.

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Old 02-12-2019, 05:05 PM   #3
RobertGary1
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Default Re: Idle questions/ gas mileage

Stuck high idle that returns on restart indicates a tps or the connector. If the rpm comes back down on its own itís not the tps.

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Old 02-12-2019, 07:32 PM   #4
fdryer
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Default Re: Idle questions/ gas mileage

Being on a budget while in college may mean short cutting needed maintenance. As a new member and maybe unfamiliar with wading thru thousands of threads to answer your questions, either read the first stickies in either the S-series general or tech forums for a short list of possibilities and real answers beyond second guessing and throwing money at unneeded parts or perform some simple procedures. The two main parts at the top of the list of must do's are the engine coolant temperature sensor and thermostat. Images below.

Remove (unless you can see which sensor is in your engine) the coolant sensor and examine it. All original sensors are plastic round nose design, cracking and sending incorrect (most often freezing temperature) signals to the pcm. The pcm in turn, runs the engine rich, sometimes flooding on startup with the temperature displaying false temps (incorrect signals sent to the pcm, pcm displays incorrect temps). The engine never runs right and as a bonus, melts the rubber seal on the t-stat. Once melted, the t-stat can't operate as coolant leaks past. Another insult to EFI systems is the engine overheats in summer weather because the faulty coolant sensor never senses coolant temps so the pcm never turns on the cooling fan. The melted t-stat seal is one example from one member with the same issues. Replacing the coolant sensor with a flat nosed brass one cures one major problem while replacing the t-stat (if its seal melted) cures another problem.

My guess is this isn't a tps issue. If you choose to wade thru forum threads, you'll see repeated issues from the faulty coolant sensor causing many problems.
Attached Images
File Type: jpg plastic-brass cts.jpg (82.3 KB, 4 views)
File Type: jpg t-stat 1.jpg (119.6 KB, 4 views)

Last edited by fdryer; 02-12-2019 at 07:38 PM..

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Old 02-12-2019, 08:27 PM   #5
JF01saturn
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Default Re: Idle questions/ gas mileage

I already replaced the engine temp sensor this morning. Iíll replace the thermostat later this week and inspect the old one.

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Old 02-12-2019, 09:44 PM   #6
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Default Re: Idle questions/ gas mileage

Ask around to borrow a reader or stop by Autozone for a free reading. A reader will display coolant temps and a fully warmed engine should be between 185F-195F. A thermometer can be inserted into the coolant container too. Presuming the replacement coolant sensor is the flat nosed brass one then the t-stat may be running cooler than normal. A reader monitoring cold engine startup should show ambient temps. The air intake temperature sensor can be used for comparison with both outputs (cold engine, ign on) within a few degrees of each other. As the engine warms up, the display should show rising coolant temps until the engine is fully warmed up.

Cold engine running will idle around 1200 rpm and gradually drop back to normal warm idle between 650-850 rpm. The coolant sensor is among other sensors that allows the pcm to adjust idle rpm throughout every mode - subfreezing startups, warm up, normal idle, ac compressor and electrical loads straining the alternator that loads the engine. The xmission torque converter and gears also places loads on the engine. The pcm detects loads from the map sensor and crank sensor (speed signal) to automatically adjust for loads.

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Old 02-12-2019, 10:34 PM   #7
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Default Re: Idle questions/ gas mileage

I have a reader Iíll give that a shot.

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Old 02-12-2019, 11:40 PM   #8
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Default Re: Idle questions/ gas mileage

The best tool in the world for post 1996 vehicles with OBD II, a reader.

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Old 02-13-2019, 09:13 AM   #9
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Default Re: Idle questions/ gas mileage

The other related point of failure is when the ECTS connector has been fouled due to the cracked sensor allowing coolant to leak through the connection. When this happens it is recommended to replace the connector making sure to solder and shrink tube the wires rather than crimp connecting. Crimp connections are a point of failure on this circuit too.

To test the thermostat without removal, start your car from a cold engine and put your hand on the lower radiator hose just after the thermostat. If it gets warm within a couple minutes then your thermostat is leaking. The thermostat does not open until the coolant temperature is about 188 F.

...
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Old 02-13-2019, 11:11 AM   #10
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Default Re: Idle questions/ gas mileage

Since this is a new to you car, you may have more than one issue going on.

ECTS/connector could be causing some of your issues, TPS another issue.

Aftermarket TPS tend to be hit and miss. I replaced my TPS a few months ago with a new aftermarket TPS to fix a high idle issue. Worked great for about 60 days and issue returned.

I sent the TPS back for warranty, but in the meantime, I went to a JY and pulled an OEM TPS. That has been working well for about two weeks.

It's weird but I noticed the OEM ones have a small dab of yellow paint on the tab.

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Old 02-15-2019, 04:14 PM   #11
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Default Re: Idle questions/ gas mileage

Quote:
Originally Posted by JF01saturn View Post
I already replaced the engine temp sensor this morning. Iíll replace the thermostat later this week and inspect the old one.
Replace the TPS, with a unit from a JY. Aftermarket TPS sensors are terrible and have very high out-of-box failure rates.

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