Got the car cheap with it running rough. Would barely hold an idle and broke up a lot (backfire, misfire etc). After spending much time and money, it ran 90% better. I replaced almost every sensor in the car. Fuel pressure checked not long ago (pump changed about 2 years ago). Put a smoke machine on the intake to check for leaks. New timing chain, tune up parts. List goes on. Anyway.. Heres my problem

After all that the car ran great. Even better at cruising speeds. But once in a while at idle, it would just shut down. No pop, no sputter, just flatline. Always started back up right away then fine for a while. Now thou, sometimes it seems to load up on gas making it hard to start. I changed the mass airflow sensor, thinking that may help knowing it is fairly common. Same problem. Just yesterday it did something that threw me off more. It started fine but after driving just a few miles, it went rough and barely wanted to move again. Once it cleared it ran fine again.

I'm thinking it has to do with the vacuum system. I had to disconect the A/C vacuum on the heater control too as it was pulling so much that it would hiss constantly (yes I tried a brand new one too).

Tired of dumping time and money into this thing when I'm probably just overlooking something. Any help would be appreciated. Oh and sorry for the long post Thanks (If it helps, I'm in NY, Maybe last few cold days didn't help either)

 

try testing the ignition moudle

 

I had put in a new pickup coil and ignition module but who knows, wouldn't be the first time I got faulty parts. Will check it out and see if that helps =) .

 

ignition module will make it stall and startup again, but shouldn't cause it to run rough... I would check EGR & CAT...

 

check your ignition and your computer. If your ecu is going it'll stall out or flood the engine or not let enough gas in. it happened with my friends 87 firebird. his ecu was going and it kept stalling out and having hard starts and when it died he found out that it was the ecu.

 

When I initally got the car, I tried a new computer with no difference in results. Ended up returning it. This problem has me good as most electric parts go bad with heat, vibration or just over time. And when they do, they are usually gone for good. Picked up a new coil and module (again). If this fixes it I know one was defective. If not, back to square one.

Btw, has anyone heard of the 2.8 cranks snapping if they backfire bad? Parts guy told me thats what happened to his. Ran fairly ok but eventually when they disassambled it, that's when they saw the crank had split.

Going to be working on it tomorrow, wish me luck... And thanks for the replies so far everyone =)

 

Quick update :

Installed the ignition coil. Started, ran great except for a little hesitation when it was cold. Went away after a few minutes of driving. Few hours later went for a drive again. After 5 or so miles of running good, I slowed down almost to a stop. When I hit the gas again, it wouldn't rev up. Pulled to the side of the road. Idled perfect but wouldn't let any gas into the engine when I opened the throttle. Checked egr and popped out the pcv valve just to see if they would affect anything. No difference.

After trying to rev it a bit more, then trying it in gear too, it just cleared up and ran great again. Was going to put a pressure tester on it but now it's fine.. No clue if its the pump, regulator or computer not opening the injectors.

Anyone know how to test these individually? Going back out there tomorrow. All I can think of is putting the pressure tester on it and running it till it goes rough again. Brain turning to mush trying to brainstorm this problem =(

 

what i found on mine was i had replaced whole distrib cap and rotor .did same thing . found wire to pick pinched between cap and distrib
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they should sell a set of noid lights at your local parts store . this is to test and see if your injectors or firing /getting power to them.

 

I think I've found it, but I can only work on the car on weekends. The MAF sensor was showing code 33, even thou I replaced it and the relay. Going to swap it for a new one just incase. The one thing that really is the problem thou, the power going from the fuse to the relay drops out just when it starts to run rough. Now I just need to trace out the wire for a bad connection. Just wondering if the other 3-4 things it connects too (Purge solenoid etc) could be shorting it out when they kick on. Electrical is my worst area on car repair but hopefully it will be easy enough. Thanks for the replies and ideas =)

 

Every little thing seemed to help a bit but in the end, replacing the ECM seemed to fix it. Brought it home now to make sure and go over everything. Runs great now, just hard to start after it sits for a while. Next step, checking fuel pressure drop and cold start module (replacing intake gaskets anyway). Ty all for your help =) .