So I would like to first say that I am sorry if something similar to this has been posted. I have been researching for quite a while and found nothing exactly like this problem.

I have a 1999 Monte with the 3100 v6. It will run fine for about 15-20 minutes. After that point it acts like it wants to die if the accelerator is pressed. It will continue to idle fine as long as you don't press the gas pedal. It isn't putting out any codes. Any help would be much appreciated.

Thanks

 

I just feel like that could be too many things. plugs/wires/fuel issues/MAF sensor/etc.

 

I second Chibi's comment. Also throw in possible coils, air and fuel filters.

So if I follow, for the first 15-20 minutes, from a COLD start (such as it sat overnight), it runs 100% fine. Then after about 15-20 minutes is when it begins mis-behaving?

If that is correct, how's the temp reading? If my memory serves, if the car just idles, it takes about 15 minutes to get to operating temp. Perhaps there is a Tstat related issue??? Just running a shot in the dark.

 

any past issue, tune ups, or parts?

 

I also agree with Chibi. There are virtually countless options.

From cold start it runs 100% for about 15-20 minutes. (It even drives normally, though I dare not drive it) Temp seems to be going no higher than is normal. The problem seems directly related to the temperature though.

It was throwing a code for the TPS. I replaced that and the code hasn't come back. Also it was reading that the EGR valve flow was insufficient. I took that off and cleaned in and around it and that code hasn't come back either.

In the past it has had the infamous Intake manifold gasket leak which was fixed, other than that just normal maintenance.

I'm actually having a friend look at it tomorrow. (He is far better at this than I could hope to be) He thinks it may be a head gasket causing a loss in compression.

 

Probably an issue with the MAF/EGR/IAC

Don't forget to check fuel pressure

 

You mentioned cleaning the EGR, but did you clean that tunnel between the EGR and the UIM? If the EGR gunked up, then sos did that tunnel. It's EASIEST to clean with the throttle body off, but I have cleaned many using a piece of old speedo cable and carb clean).

Best of luck, hope an answer is easily found!

 

Check your catylitic converter to they can plug up or break loose on the inside then plug the muffler

 

I don't have much experience with failing cats, but the ones I have had experiences with, hot/cold, it doesn't matter, car runs for crap from the start (lose of power).

I'd put the cat on the list, but given the symptoms tie to temp, I'd place it as a lower item to check.

 

Ok so I did a few things with it today. I replaced the fuel filter, bought a new coil pack and used it in place of each to see if one was bad and causing the problem(I will probably replace them all anyway.) I took off and cleaned the MAF sensor with some spray cleaner. Tomorrow Im going to try to go get a fuel pressure gauge and see if it could be a failing fuel pump or something.

I have decided that the head gasket is probably going bad as it seems to be leaking coolant very slowly. (it doesn't have any signs of coolant in the oil though so I'm not sure). Also I talked to my Uncle who is a very good mechanic. He doubts strongly that a bad head gasket would cause it to do this. It wouldn't run right at all if it was losing compression from the gasket. (slim chance anyway, still praying its not the head gasket) He also is saying that it could be the ignition control module. (would that put off an error code?)

When I cleaned the EGR valve i did clean down into the pipe. Maybe I didn't clean low enough into the pipe. Ill check that tomorrow.

What would be a good way to test the IAC?