My 86 IROC (305 tpi) gets a code 32 whenever the engine is at a steady rpm (usually about 2000)running down the interstate on the way home. It comes on after the engine is good and warm and the rpm has been steady for about 5 or 6 minutes. I've noticed on days when the road is full of folks that don't know what the left lane is for the code 32 never lights up as the rpm varies while passing them in the right lane. I've also tried purposely varying the rpm while running down the interstate and don't get a code 32 then either so it's something about running a steady rpm. Oh, I have no mufflers either, just large pipes from the catalytic converor back to the normal dual exhaust outlet position in the rear so the exhaust back pressure should be pretty low. Seems like someone else reported a similar problem earlier. Just a (long) comment in case anyone else runs into the same thing.

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Z's r Best

 

I dont know if you saw my post about this, but I had the same exact problem a while back. Same EXACT situations as yours(with the exception that i have a full performance exhaust)....it was between a constant 65-70mph speed that my service engine light came on...and it could stay on anywhere between 2-45 minutes or more, then shut off and never come back again. This happend only on long trips, never on distances shorter than 30miles. There are three possibilites that could be at fault: EGR valve, barometric pressure sensor circut failure, or something with the vacumn lines. Everyone told me when i posted about this problem to check the EGR first. I havent gotten to it, mainly because i have no time or $$ right now to do anything. But i will this summer. Some of the symptoms i have also experienced is mostly when the engine is cold, the car does not want to stay started...stalls a couple times and then finally, stays on. This sometimes also happens when the engine is warm. And when running the car, at a stop sign or light, the RPM's die down to well below 1,000...look for these probs, and also check the EGR valve and vacumn lines. Hope this helps. Good luck, and post your results.

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1986 WS6-Equipped 5.0 TPI Trans Am
Random Tech High-Flow Cat
Two Chamber Flowmaster Muffler
Megs Custom 4.5" Stainless Steel Rolled Tips
1999 Grand Am GT In-Dash CD Player w/Equalizer(fits like '86 original)
5% Tint On Rear, 35% On Sides
http://www.pitt.edu/~zyhst/trans86/

OTHER RIDE:
1998 C5 6Spd. Corvette Coupe
Silver w/Gray Leather Int.
12/14 Options
Stock(for now)
Best 1/4th: 13.5 @ 104.4MPH

 

Well to go on what i have been doing, If you have no mufflers , and you have a negative pressure valve, then that would be your problem , because those egr valves us eback pressure from the exhuast , To check , when you pull your plenum off , there be either a P or an N at the end of the part number. if its an N put a muffler on , if it started after you pulled the muffler off, then i would suspect that would be it