Al90IROC6

ok so I have been searching through all the threads and am at a loss. My '90 Iroc with a 305 TPI likes to stumble and stall sometimes when hot. It happens at low speeds in traffic or in a parking lot. Ill be at around 1000 to 1500 rpms and let off the gas and it boggs down to 200 or less rpms and sometime stalls out. I have removed and cleaned the IAC, checked the TPS, and ohmed out the injectors hot and cold. TPS was at .59V closed and 4.3V wot. Injectors 16.2-16.6 cold and 17.2-17.5 ohms hot. Timing has been set to 6 degrees. Off idle and driving it drives great, no issues. Only when at low speeds does it start to act up. Any insight would be greatly appreciated. Oh and no codes when checked.

rusty vango

a really complete tune up. could be in order. how old is your ICM? and im finding that although the TPS does have a little wiggle room, they seem to work best set at .5v at idle. and you should be seeing 5v at WOT. any deviation from these specs will cause what you describe.

Al90IROC6

ICM is about 4-5 years old, same with distributor. Ill try playing with the TPS and see what happens.

IROCgiraffe

iTrader: (3)

I've got similar symptoms.. and plan on replacing my distributor with an MSD unit. The contacts on the inside the cap and rotor on mine look good. I've already replaced all the simple stuff with AC Delco, i.e. TPS, IAC, plugs, etc....

Al90IROC6

well if it fixes it Im going to feel dumb. I took the cap off to check ac voltage out of the pick up coil and found green corrosion on all the terminals inside the cap and the rotor as well. so I have one coming for this afternoon. we will see. Thanks for the replies!

rusty vango

believe me, its better to FEEL dumb, than to BE dumb. and green corrosion is a big no no as far as ignition components go. it may well be all you have to do to get it right.good luck and post what your results are.

Al90IROC6

Yea right as I took it off and saw it I kicked myself for no checking that first. Forgetting the basics.... Ill post again when I have it situated.
Thanks again!

Al90IROC6

well put the new cap and rotor on and it definitely runs better, but still surges down and stalls at low idle

Al90IROC6

feels like a fuel issue. going to check fuel pressure and see if I have a leaky or clogged injector

rusty vango

a clogged injector would give a dead cylinder. and a leaky one would make it have a hi idle speed and smell rich. re set your TPS and see how it does.

Al90IROC6

I will try the TPS. I checked fuel pressure and it is at 36psi at idle and 46psi with the vacuum line off the regulator. when I shut it off the car pressure drops 20 psi in 30 seconds. regulator and pump are about 3.5 yrs old.

rusty vango

in the tank, there this thing ,a "pulsator". it goes between the FP and the pipe on the sending unit. with a pressure drop like that.sometimes you will find that rubber piece has gone bad. of course you should see if your regulator is leaking as well. that could also be an issue .

Al90IROC6

thanks. Just used am EFI probe tool while car was running and when it started to stumble found that #5 injector would cut out randomly. Gonna need to save some cash and get some bosch 3's!

rusty vango

well, there you have it. another happy customer!!!!

Al90IROC6

yup thanks for your help