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Originally Posted by Fireplug
What was the engine temp at time of test and at what rpms was the test made. I would remove and clean the idle air control valve and clean the throttle body.
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Fireplug,
I'm assuming that you mean my engine temperature during the emissions test....If that is the case, my engine was very warm as I have a 45 minute highway drive to the emissions facility. The emissions test has a profile that varies speed and acceleration from stop to highway speeds, down to low speed, back to highway speeds and down again. Some require the tester to slowly take off, stomp on the gas, and fully remove his foot from the accelerator. It is during these slow take-off speeds and when the foot is removed from the accelerator that the high hydrocarbons are present; most notably at lower RPMs.
I've applied 4 bottles of GM Top Enginer Cleaner cleaning the throttle body inside and out thoroughly. I've taken off the IAC valve and cleaned it (it had a build-up of soft carbon on its conical nose) to no avail. I've also viewed the IAC valve through the top of the TBI unit (with the air cleaner housing removed) while in operation and can see it opening up during periods of high RPMs when my wife hits the accelerator...and closes the gap when decelerating.
Any other suggestions?