Alright guys i have been having this problem for about 9 months now, however my ar sits at home while im at college so i havent had a chance to fix it.

Near the end of last summer i started to have the problems. Engine would miss fire and stumble all over only once the engine warmed up and switched from open/closed loop. It ran so rich it made my eyes tear up when in the back. Once this started it would have a really bad idle and just die off.

Now to try and fix this problem i replaced the 02 sensors, MAP sensor and a bunh of others header gaskets, fixed the ehaust leak, found the EGR tube cracked and blocked it off, spark plugs and wires, checked the fuel pressure, fuel filter, new injectors, and a few other things and nothing got better.

When i returned from college for a one moth christmas break the car ran PERFECT in the cold weather (michigan). So the problem only happens in warmer weather and not old weather.

So i started my car up yesterday and the problems are back. The opti i have was replaced about 6k miles ago with a GM one from james crommer. So what the hell is my problem? maybe the MAF becuase it only happens in the cold? the coil? the opti? what is it? I cant depend on my Yamaha r6 during the spring (rain) and i need my car to run right. Please any help would be awsome.

my car is a 94, 62,000 miles, manual if it matters

Would a bad MAF do this?
here is my logic

cold weather- Dense air requires more higher fuel for the air/fuel ratio
warm weather- less dense air requires less fuel for the air/fuel ratio

So in the winter it runs fine rich beause the dense air. During the warm summer when it runs rich it fouls out the spark plugs... this sound at all right?

 

If you have access to a scan tool, check what the ecm is seeing for coolant temp and intake air temp. I'm leaning more towards a problem with your coolant temp sensor. If the ecm thinks the coolant is cold, it is going to richen the mixture. This is great if it is actually cold (like a cold start on a 30 degree day...possibly why it ran ok last winter), but when the coolant is actually warm or even ambient temp on a warmer say 70 degree day, this is a very bad thing. The richer fuel mixture will load up the plugs causing missfiring etc...

If you suspect a bad maf, unplug it and start it up. The ecm will realize there is a problem with the maf and use inputs from the tps and map along with engine rpm to "guess" at what the air flow actually is. It won't run great and you'll get a check engine light almost immediately, but it will run better than with a maf that is sending the incorrect signal.

hope that helps

 

i will do that. i already replaced the coolant temp sensor...

 

any more i9deas? i have to go to a funeral on saturday and i will try some stuff after and give an update... please any help will be appreiated

 

Hey white phoenix if you solve your missfire, pm me your solution! I have the same symptoms as you- my car runs great in open loop or when its cold outside. After 5 minutes of driving in warm temps I get the po300 code and I can barely limp home. That first 5 minutes it runs great though, I replaced fuel pump and pressure is good, new plugs and wires and fuel filter. My maf is descreened, do you think that would contribute my missfire?