Rough engine 1500-2500-neutral and in gear - LS1TECH - Camaro and Firebird Forum Discussion

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Rough engine 1500-2500-neutral and in gear


Old 04-16-2018, 07:47 PM
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Join Date: Feb 2015
Location: Roseland, NJ 07068
Posts: 20
Default Rough engine 1500-2500-neutral and in gear

My 2002 5.7 Camaro SS, auto trans, had a condition that felt like misfires at mostly 1500 RPM and then 2100 RPM while in neutral or in gear. To make matters worse, it would not drop into the overdrive mode in 4th gear and you could feel the vibration while decelerating. In addition I would get code PO420 which usually indicates a catalyst condition but can also be related to many other conditions which eventually run down through the cat. I read all the previous posts which resulted in even more confusion for an amateur like me to comprehend from bent push rods to harmonic balancer. My particular car had a very hard life as a street racer disguised as a stock 5.7 auto trans slug. I figured that there most probably had been various combustibles other than pump gas run through the injection system. Sure enough the throttle body was soot black, front & back, and the Idle Control Valve was completely covered with the same black soot. I figured this was from misfires created by different additives. Car ran very rough but still managed to go quite well at WOT. After reading many different forum posts for GM and other brands including imports, I took a shot and replaced the following small parts which can easily be overlooked. I replaced the Idle Control Valve #17113598 and the Throttle Position Sensor #213-4668. I also did a complete cleaning of the throttle body and sensor screen. Whoa, day and night difference. Engine at any speed is now smooth as it should be and lo and behold it glides into 4th gear overdrive. No codes. I should warn you that upon first start-up the engine will jump up to a 3,000 RPM idle if you don't give the PCM enough time to recognize the new part before engaging starter. Total parts cost for original AC Delco was about $125 via Amazon. Hopefully this will help some of those who are chasing these same rough engine ghosts.

Last edited by Redrokit8; 04-16-2018 at 07:48 PM. Reason: spelling
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