2002 SC1, 5 speed, 1.9 L Rough/High Idle - 75,000 mi

SAMUELRODGERS

MEMBER
2002 ALL OTHER MAKES ALL OTHER MODELS

I have replaced just about every sensor on this: ECTS, Air TS, IAC, TPS, MAP, inlet O2 sensor. New plugs and wires. Checked for vacuum leaks. If I start it cold and just let it idle, it will quickly drop to 1200 rpm in less than a minute, the hunt down lower in RPM to about 1000. It is missing a little at that lower speed. After that, it will in a few minutes rise back up to 1200, then 1300, then 1400 rpm. If I start driving then the minimum idle during a shift will pop up to as much as 2000 rpm, as if it is cold. As soon as I stop at a light the rpm will drop to 1300-1400 again. It doesn't seem to be missing at the higher idle rpm and still gets great mileage. I got 36 mpg on my last 4 hour drive.

Besides what could be wrong, does the outlet O2 sensor have anything to do with idle rpm on this engine, or is it only tied to the cat failure sensor? I haven't replaced it yet. :

3 Replies

PEPPERMRJ

MECHANIC
1,158 POSTS

Hey Sam,

Sounds like you have gotten to know this Satty very well. The downstream O2 only monitors the cats performance.

Do you have any trouble codes?

Did you clean the throttle body and IAC port when you replaced the IAC and TPS. Sometimes a little gunk can cause problems.

Might also have a dirty EGR port and pintle. This would account for the low speed miss possibly. Easy to clean just remove and use an old toothbrush with some throttle body cleaner.

I would also check the ground for the coils and DIS module. Remove them and check the plate they mount to and the bolts for corrosion. They like to be squeaky clean.

Did you use OEM parts? I have seen a few aftermarket replacement parts bad out of the box. Plus check the connections for the sensors. Make sure they are clean and tight.

Good hunting and let us know. :)
peppermrj

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Tuesday, April 24th, 2007 AT 11:16 AM

SAMUELRODGERS

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Only trouble code is high idle, which will reset if I leave the AC on for a few starts. The idle is normal with the AC on.

I used a toothbrush to clean out the IAC seat when I replaced it and sprayed lots of cleaner and brushed the throttle body. Also used cleaner and brush on the EGR valve. I also tried plugging the EGR port off with a solid gasket during idle with the same high idle problem.

I have not checked the coils other than resistance across coil + wires and just coil. Both were in specs.

When I borrowed a scan tool, the data when high idle code set showed the fuel settings both short and long term as negative numbers (-8 to -10), which I believe means that it thinks it runs rich and has to be leaned out.

How long does it take to reset the computer with a new O2 sensor if you don't power-off the computer? Should I try that?

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Friday, April 27th, 2007 AT 9:27 PM

PEPPERMRJ

MECHANIC
1,158 POSTS

Hey Sam,

I would clear the code with a scan tool and then disconnect the computer. It should relearn with about 50 mto 60 miles of mixed driving.

Good luck and let us know. :)
peppermrj

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Saturday, May 5th, 2007 AT 10:38 PM