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Intermittent idle problem

Saturn SC1, 175,000 miles. Car runs fine except for at random times the idle will climb to 1300 rpms I think when hot but intermittent so I’m not sure. On test drive when stopped at a stop sign the idle will be 500 but almost stalls. Fuel pressure regulator is intragle with the fuel filter and I am getting constant 42 lbs fuel pressure which is a Little low but not bad. So fuel pressure regulation isn’t the problem. The Stft was -20 so it’s running rich. I removed throttle body and cleaned it. Checked all vacuum lines. Started and idled for a while and fuel trims we’re good. Then the idle climbed again and fuel trim dropped. Temp sensor is working. No codes. From process of elimination I’m thinking iac but I don’t think that would make it run rich. My next thought is MAP sensor but the readings change when I change rpms. I don’t want to shot gun this. Any ideas?

Sounds like the EGR valve is leaking. Lets extra EGR gas into the intake looking for more fuel to settle the fuel trim. EGR clogging was a problem on these cars especially, if I remember correctly. THe EGR is electric and probably still working since no code has been set. Remove it and get a good look at the passage. Clean as needed.

It may also have a vacuum leak between the MAF and the engine. Normally not intermittent but stranger things have happened.

Thank you. Will try that next. At least it’s easy to get to.

Since you don’t provide the year of your Saturn, it’s impossible to look up any TSB’s that may relate to your problem. :roll_eyes:

Tester

Sorry it’s a2001. I included it on the header but it didn’t show up.

It sounds like the Idle Air Control valve is hunting for the proper idle speed.

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Tester

All SC1 cars had the 1.9 SOHC engine. SC2’s the DOHC 1.9. The first was built in 1991. The last SC was built in 2002. GM then made them corporate derivatives.

The map uses a nipple that inserts into the manifold. I removed the map and introduced vacuum to the nipple. With KOEO the scanner matched the vacuum I supplied. So I officially ruled out map. I actuated the egr with engine running and it responded as it should. When I actuate the EGR my scanner automatically raised RPM to 1500. But when I opened the EGR to 40 -50% the fuel trims matched the trims I had when the idle raised on it’s own so I cleaned the EGR. I didn’t experience any problems after that except for once, but that’s when I was playing with the scantool. The STFT is still -11, a little low but better than-50. I will drive it for a couple days and see how it goes.

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That was my first thought, but would a malfunctioning IAC cause a rich condition?

Oh?

I must have misread your post.

I thought we were discussing an idle problem?

Tester

Sometimes I don’t come across real clear. It is an idle problem. It will idle normally with slightly low STFT. Then at random times the idle will surge to 1300 rpms (around). During the surge the STFT will go to -30 to -50. I don’t think an IAC will do this, but I don’t know for sure.