I have a 1999 Saturn SL2 with a 5 speed that idles normally until I start to drive it, then the idle runs anywhere from 1800 to 3200. At this point I have cleaned the throttle body, IAC, and the entire upper plenum. At this point I have run out of ideas. Any sugestions?

 

Throttle cable binding/slacking?


Throttle plate not moving freely back to "rest" position?


Vacuum leak?


Check around throttle body and intake manifold by spraying with throttle body cleaner -- listen for changes in idle while doing it.


Any codes (SES)?

 

I did use both propane and carb cleaner to check all hose connections and manifold gasket areas for vacuum leaks and found none. The cable is free and moves easily. I cleaned the throttle plate and the throttle housing.


The car has no current or history codes stored in the computer and the light is off. According to the scanner when the engine is running at 1800 RPM the computer states that the desired idle is supposed to be 950.


Is it possible that the computer needs to be reburned and reprogrammed to elimiate this condition? Or is there another component to the idle control system that I have not checked causing this to happen?

 

Pretty whack....

ECTS is a possibility but the idle speeds are usually not quite so bizzarre.....

If it is the "idle" that is far out of kilter, it will set an "Idle out of range high" code to acknowledge that the PCM cannot properly control the idle speed.

However, you indicate that this only seems to be a problem when the car is in motion, not when idling at rest. The car will not return to base idle speed while it is still in motion -- but it should come much closer than that....Vehicle speed sensor-related?
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I want to say DIS module but it would almost certainly throw a code and would probably not act differently when the car was in motion versus at rest... (?)

Throttle position sensor?
PCV valve sticking?

MAYBE something to do with an EGR sticking open problem?(though it really does not sound like your typical S car EGR problem)

Reaching.............