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Old 04-15-2013, 01:09 PM   #1
qazu2005
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2000 SL2
Default Rough Idle/Engine sputter 2000 sl2 dohc

Hey all, I have been reading and using these forums for quite a while, and now I finally have an issue that I simply have not been able to figure out just by reading. Hoping I can get some advice or a pointer in the right direction.

Car is a 2000 sl2, 1.9L dohc, 151k miles, manual transmission. I have owned the car for a little over 6 years.

Over the last 6-8 months this issue has been occurring...intermittent rough idle, more vibration than usual when at idle. When the engine is first started, it idles high between 1200-1300 rpm, but as the engine warms up it drops a bit down to around 1000-1100, which is still higher than I think it should be, although the car has always idled a little high since I bought it.

Also, when first starting the engine, or when it is returning to idle, it will sometimes sputter and almost die, then bounce around a bit and finally even back out to around 1100-1200 rpm. When accelerating or keeping load on the engine, there are no noticeable issues or loss of power. The problem seems to only occur when idling/returning to idle.

Here is a list of what I have done to the car so far trying to resolve this:
New iacv
new tps
cleaned throttle body
cleaned egr valve (I could hear the valve rattle so I don't think it's stuck)
new oem ngk plugs (the plugs I took out were actually still in good shape...but figured it couldn't hurt to try)
new wires
new fuel filter
cleaned fuel injectors
new air filter
new pcv valve and grommet

I also did seafoam through the pcv hose last week to see if that helped at all. This did make the engine idle beautifully for about 7-8 minutes and then it went back to doing to same thing once all the seafoam worked it's way out.

I have tried looking for vacuum leaks using the carb cleaner method, but so far have turned up nothing.

I'm pretty much at a loss now as far as what to try next. No codes have been thrown other than one random misfire one time when the engine sputtered really bad.

From what I have read, it sounds like the ects could possibly trigger symptoms like this...is this a possibility? And can the ects be bad without triggering a code? FWIW the engine has always run relatively cool (temp gauge always stays right around the 1/4 mark when warmed up). Car has never overheated or gotten really hot except for one time when the serpentine belt got knocked loose and I didn't realize it. That was over two years ago.

I know that low compression can cause misfires and rough running right? But I'm also thinking that if it were losing compression somewhere, wouldn't there be symptoms other than just at idle?

Also fwiw, I have new coils on order and will put them in this weekend.

Any advice or pointers in the right direction would be much appreciated.

Last edited by qazu2005; 04-15-2013 at 01:21 PM..

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Old 04-15-2013, 05:23 PM   #2
lamping.ap
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Default Re: Rough Idle/Engine sputter 2000 sl2 dohc

Have you checked the connector for the ects?

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Old 04-15-2013, 05:32 PM   #3
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Default Re: Rough Idle/Engine sputter 2000 sl2 dohc

Also check the ect sensor itself and make sure it has a brass tip on it. Yes, the coolant sensor can cause driveability issues, it directly controls the air/fuel mixture. It's possible the thermostat may not be functioning correctly as well but check the ects first and go from there seeing as how it controls the gauge reading.

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Old 04-15-2013, 06:36 PM   #4
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Default Re: Rough Idle/Engine sputter 2000 sl2 dohc

A picture or two will help. Replace the plastic one immediately. You will be rewarded with instant starting, faster warm up, and a return to normal idle once again (800-900 rpm). You might have to replace the thermostat if the temperature doesn't stay above the 3/8ths level or heater isn't as hot as it once was.
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File Type: jpg plastic cts.jpg (38.0 KB, 23 views)
File Type: jpg brass cts.jpg (28.3 KB, 18 views)

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Old 04-15-2013, 06:50 PM   #5
qazu2005
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2000 SL2
Default Re: Rough Idle/Engine sputter 2000 sl2 dohc

Thanks guys. I guess my next step will definitely be to replace the ects.

I guess I'm a little unsure about the thermostat as far as whether or not I should replace that too. My temp gauge has historically stayed just a hair over the 1/4 mark (fully warmed up) for as long as I can remember. I've seen it creep up to the 3/8 area, but usually only when I'm climbing steep hills or similar conditions. I guess I just assumed the 1/4 mark was normal for my car until I started doing a little more reading on here. So here's a couple questions:

If the temp is always hovering around around the 1/4 mark, is this always a 100% sure sign that the t-stat should be replaced?

If not, what other ways are there to tell for sure?

My heater has always worked well, although I'm not sure if the fact that I live in the middle of the desert in southern AZ is a factor there or not...in the middle of winter it is rare to see ambient temps below the mid-30s (F), even for a nightly low. So maybe my heater performs well enough for those conditions, but wouldn't perform as well in a colder place?

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Old 04-15-2013, 08:03 PM   #6
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Default Re: Rough Idle/Engine sputter 2000 sl2 dohc

The coolant sensor is famous for failing first. Its also the only sensor that communicates temperature signals to the pcm. The t-stat doesn't but does regulate overall coolant temps for EFI system efficiency. Both parts are intertwined, one to talk to the pcm while the other regulates overall coolant temps as well as influence the sensor. Screw with one, the other or both and Saturnfans is littered with repeating issues surrounding these two parts.

Where you live you can almost ignore replacing the t-stat simply because you aren't in freezing regions needing heat nor need a hot running engine. 195F has been the highest t-stat used to raise coolant temps as high as possible to squeeze as much energy from fuel that's already wasted as heat in oil, coolant, and exhaust.

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Old 04-15-2013, 08:23 PM   #7
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Default Re: Rough Idle/Engine sputter 2000 sl2 dohc

I'm thinking maybe this weekend I will just go ahead and replace them both. Been wanting to do a coolant flush anyway, so it's as good a time as any to knock them both out. The sensor should be a snap to replace from what I've read, but can you point me toward a good guide on how to do the thermostat? I tried clicking on the one in the new/returning owners sticky but I think the link is bad?

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Old 04-16-2013, 12:10 AM   #8
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Default Re: Rough Idle/Engine sputter 2000 sl2 dohc

T-stats are generally a two-bolt affair and yours is just below the a/c compressor. The bolts sometimes seize if not unfastened since new car buy so some may require more drastic measures like a bolt remover that grabs what left of a rounded hex head to make life less stressful. One member mentions to bang the bolt heads a few times to help loosen the hardened loctite or anything that would act as a thread lock. Always worth a try as it won't hurt anything and may save you from some grief. Flushing first; drop the lower radiator hose to drain coolant and reattach to fill up with plain water and either warm up the engine or drive around the block before draining for either another flush or continue with removing the t-stat housing, clean off any gasket left on surfaces, replace the t-stat, bolt everything back, refill with fresh coolant. The coolant sensor can be replaced when coolant is drained.

Last edited by fdryer; 04-16-2013 at 12:21 AM..

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Old 04-16-2013, 01:20 AM   #9
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Default Re: Rough Idle/Engine sputter 2000 sl2 dohc

A few light to medium raps on the tstat housing bolts may be ok if you are an accurate shot, but banging should be avoided so as not to crack the housing. Ask me how I know.... Better to just use a good six point 10mm socket and make sure you are completely on the bolt head before your first turn.

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Old 04-16-2013, 09:20 PM   #10
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Default Re: Rough Idle/Engine sputter 2000 sl2 dohc

Thanks for the advice and tips. I will do the R&R this weekend and see how it goes!

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Old 04-17-2013, 08:50 PM   #11
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Default Re: Rough Idle/Engine sputter 2000 sl2 dohc

Ok sorry couple more questions before I do this job:

1. Is there any other gasket I need for the t-stat and/or housing other than the round ring?

2. Does the ects function as both the sensor and sender on my car (2000 sl2)? From what I can tell I guess it does since I can't find a separate temp sender anywhere.

3. Should I refill system after flush with Peak long-life or stick with dex-cool? From what I've read the Peak should be fine right?

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Old 04-17-2013, 09:11 PM   #12
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Default Re: Rough Idle/Engine sputter 2000 sl2 dohc

T- stat needs a gasket. And yes the ects does double duty, both temperature sensor and signal for the PCM to display coolant temperature and for the PCM to determine fuel/air mixtures. When flushing a cooling system, use whatever you like as long as its a 50/50 mix.

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Old 04-21-2013, 10:50 AM   #13
qazu2005
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Default Re: Rough Idle/Engine sputter 2000 sl2 dohc

Well yesterday I did the coolant flush and the R&R of the t-stat and ects. Operation was a total success!!! Turned out to be a pretty easy job. Even the bolts on the thermostat housing came out easily. The old ects was most definitely completely shot...it was the original one, and was cracked in multiple places. Looked like a little grand canyon running down the middle of it on one side.

I tried re-using the ects connector at first, but I realized it was bad when the temp gauge started jumping back and forth between C and the 3/8 mark. So I just soldered in a 2-wire pc connector and now life is good! I have my nice smooth idle back at 850 rpm, and my warmed-up temp is holding steady right at 3/8 mark. Thanks everyone for your help!

Last edited by qazu2005; 04-21-2013 at 10:56 AM..

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