The car runs fine and idles fine until after about 15 min. of driving. After that it will start missing. If I let off the gas it will clear up. I can then give it gas again and it will run fine for a bit until the next miss "episode" when I have to do the same thing again. Are these symptoms of a dirty injector? I figured it it were spark related, like a plug wire laying on a header, it would continue to miss and not clear up when the throttle changes. If you think it is an injector, how do I take it apart and clean it out?

 

Hmm sound like something related to closed loop operation, how is it missing? Is it hicupping or studdering when you press the gas? If you had a miss on one cylinder you would know, its pretty obvious. If the MAF is not acting right USUALLY the engine coughs or backfires when you press the gas, then goes back to normal when you let off. A bad O2 sensor or open wire can also make the engine seem like its missing since it fools the engine to think its running lean. So the PCM dumps a ton of fuel in and makes the car run like crap, but it wont do it untill the engine heats up and goes into closed loop, also you would smell a ton of unburnt fuel. Hope this helps.

A dirty injector would probally make the car run crappy all the time regaurdless of running time or temp.

 

Sleeper, this is the kind of info I am needing right now. I'm having the coughing(seems like its missing) engine symptoms. I've troubleshot the ignition system and ruled it out. I'm going to focus on the MAF tomorrow. Thanks.

 

I'm having the same problem
after I've been on the highway for 10-15 minutes it will sputter like it's loosing power. It's starting to do it in the city now too. I can't figure it out quite yet

 

Check the Evap Purge system.
I know one guy who with a new fuel pump was "running out of fuel" but a few moments of being shut off and the problem would fix itself.
Vacuum was building in the fuel tank as fuel was pumped out and no air was replacing it. Eventually it would overcome the fuel pumps ability to pump and it would "run out of gas".

Loosen the fuel cap a little and see if the problem improves as a check for this.

 

Well, I could be wrong, but if it were a closed loop problem, wouldn't it do it sooner than 15 min. into driving? I thought the car goes into closed loop relativley qucik, i.e. 1 min. max? But, maybe we need a PCM expert to chime in on that.

To answer your question, the throttle position will not change, mantaining a cruising speed of around 70 MPH and about 1600 RPM's, and all of the sudden the car will loose a ton of power and start stuttering until you let off the throttle. After you let off it clears up and you can give it more throttle. The car hasn't backfired yet. I just replaced the O2 sensors about 2 months ago, but the problem started about a week ago. The car ran fine after the new O2's.

I'll try the gas cap idea and see what happens. Is this the only way to check the EVAP system? Thanks for the advice.

 

Does it take 15 min if the engine is completely cold or does when hot also. the PCM wont go into closed loop untill the engine hits a certain temp.

Do you have O2 extentions for your headers, im not familiar with Kook's headers but if so, there could be a bad connection in there. O2s read millivolts so there are very sensitve to resistance. I recently had a problem similar to this so I hooked up a scanner and drove around. I had some sort of intermitant open circuit on the right side O2.

I think a scanner would most likely show you whats going on.

 

The headers do have extensions on them. I'll check that for a good connection. As far as the car hitting closed loop at a certain temperature, I have an 160* thermostat and an electric water pump, so even in the summer, the temperature never gets above 170-175. So at what temperature does it hit closed loop? Also, another similar thread with the same problems said something about changing out the ICM. Car has 150,000 miles on it, I bought it used at 82,000 miles and as far as I know, the ICM has never been changed. MIGHT this be the problem? Guess it wouldn't hurt to change it out for peace-of-mind.

sleeper94z28, your absolutly right, I need a scanner. Maybe instead of the next performance part, I should invest in a scanner and cable for the laptop. Because it has given me a SES light durin this whole ordeal, but it only stays on for like 2 min. and then goes off. But, if I understand correctly, the computer stores codes for a little while. Thanks for the help. As soon as I figure it out, I'll post what I did.

 

You can read DTCs without a scanner, I dont remember what exact pins it is but if you use a jumper wire or a paper clip you can jump 2 pins on the OBD port and the SES light will blink a a certain number of times. count the blinks and write the number down, that is the DTC code. A Chilton's manuel explains all of this but im sure some one on this forum knows too. Do a search and i bet you can find out exactly how to do it along with a list of the DTCs.

From a past experience I had the SES light come on for a couple of min on the highway then shut off when I came to a stop. When I got my scanner it was the O2 sensor.

 

Opps nevermind, one of my buddies said you cant use a paper clip on 1994 and up cars. I guess your gonna have to get AKM cable and FreeScan to check it out. TTS DataMaster is also an awesome investment and has helped me out countless times. The best part is that they give you 10 free recordings before you have to buy it.

For a cheap cable go to Steve Ruse Electronics for 65$
AKM cables is like 95$
FreeScan is like the name says...FREE
TTS is 95$ I think from AKMcables.com

My car runs the same temp too, about 175, so im sure its going into closed loop. Also my car have 154000 miles and im still running the stock ICM, but im not saying yours isnt bad.