HeavyHook

My 86 Iroc started having a rough idle about 6 months ago and has developed into it missing as I accelerate. The engine still has good power but it has started to stall and after its warm it does not want to idle. I have checked the normal stuff plugs,wires distributor and cap. I have even checked the IAC but its working fine. The new crate motor only has 10 K in the last three years on it. I have searched through all the vacuum hoses because it acts like a bad leak but I can't find anything there. The only thing That I have found is that the solenoid in top of the vapor canister is so hot that you can not hold your hand on it but for a few seconds.but Im not sure if that could be a problem or not . Please help Guys!!!!

Rice Killer87

i see that no1 else has replied to this so ill try to help u out...
how about injectors? are they big enough,clean,and are the connectors attached tight?

have u pulled the spark plugs and looked at them?

how about the convertor,is it gutted? if not,could be starting to come apart inside.
hope this helps

TheGreatJ

Tap hard on the cat with a rubber mallet. If it rattles that's your problem.

The evap solenoid shouldn't cause it to miss cylinders altogether, but it can cause bogging and rough idle problems.

90rocz

Here's my experiences with hard to find misses.

1) One plug was firing way rich, fouled. I switched the plug wire with a different cylinder, still missed. I swapped out the cap & rotor button, still missed. I then swapped the fuel injector with a different cylinder, still missed. Finally I swapped the computer, BINGO! smoothed out, problem solved.

2)My cuz had an '87 Black & Gold Iroc with a bad miss that got worse under acceleration. No fouled plugs(not real bad). We checked for vacuum leaks. We swapped the cap & rotor and replaced plugs and wires. We finally did a compression test and 3 cylinders were LOW for compression. After pulling the valve covers and intake, we found bent push rods and collapsed lifters. We replaced them, problem solved.
(( If you roll a push rod on a piece of glass and hear a "womp-womp" sound, they're bent. Lifters often get gummed up and either collaps or turn into solid lifters, not preloading. Either way it causes a miss and sometimes rattling.))

87IROC-Zowner

Fuel Pressure.

Stopped up fuel filter can cause numberous problems and an old fuel pump loses its ability to feed enough volume to the engine. Although it may have plenty of pressure, you need to check the amount of fuel it is actually supplying in a given amount of time.

HeavyHook

I have looked at most of the things that have been suggested. The motor was a brand new HO GM 300hp/350 grate motor and has only 10K on it. The fule tank was off after and cleaned out the engine swap to put in the holly fule pump and at the same time the fule filter was changed. I would think if I had crud in the filter or low pressure the car would not accelerate good which it still does whin I nail the throttel. The orginal #19 fule injectors were replaced with a new set of #22 lb when I took the 305 out and replaced it with the high output 350. Oh about the cat suggestion I punched that dude out durning the engine swap three years ago. The first things I did check though was the plugs wires cap rotor ,for fule leaks vacuum leaks. I dont thinknit is a computer problem because it has started out as a minor thing and has just gotten worse over time. I have computer that pulls all the info out of the on board one (not a code puller) it gives me the counts the injectors are firing,IAC counts , O2 oms ect. but I really do not see anything out of wack there. Thanks for the suggestions so far and anyone else that has a Idea. One thing I know is for sure on these 3rd gen cars is that someone else has had this problem too.