My sister has a ‘99 Bonnie with the standard 3.8. She has been having problems with it stalling as soon as the engine warms up to operating temperature. The first time she cranks it for the day, it has a rough idle til it warms up and stalls. The second time she cranks it, it’ll start right up and idle smoothly until it stalls (a few minutes after she cranks it). However, when she tries cranking it a third time, it won’t start right up...she has to wait a couple of minutes or so for it to cool down a little bit then it’ll start...but stalls again shortly after. The following is a list of things she has already done but obviously to no avail:

Changed:

-Plugs and wires

-Fuel filter

-Fuel pump

-Crank sensor

-Camshaft sensor

-EGR valve

-Checked catalytic converter temp

She just check the codes and it was showing four different codes:

Code Description

• P1676 stored(1/4)- driver 4 line 6
• P0102 stored(2/4)- MAF circuit low frequency
• P0742 stored(3/4)- TCC system stuck on
• P0102 pending(4/4)- MAF circuit low frequency

Any ideas? Before the codes were checked, I was thinking the MAF. However when she told me the rough idle wasn’t all the time, and it stalls at warm temperature I then started thinking about a bad coil. She’* in the process of cleaning the MAF to see if that helps a little. Thanks in advance for the advice.

Disconnect the MAF and see if it starts/runs any better.

You never mentioned cleaning the IAC valve.

Clear out the codes and see which ones come back.

I just talked with her and she said that when she went to crank it, it would not start. However when she went ahead and disconnected the MAF, it started right up. The idle wasn’t rough like it had been. She turned it off. Plugged it back up and it would start but idle was a little rough once the computer “realized” it was plugged back up.

Haven’t tried cleaning the IAC valve yet. I tell her to clear them out. Thanks for the reply.

Sounds like typical MAF failure. Stay away from the cheap ones if you can. They have a higher failure rate than the OEM ones.

These GM MAF sensors have an internal fault that creates problems. With the engine idling tap on the sensor and it the engine stumbles or stalls it'* bad. Sounds like you found the problem.

She just pulled the IAC valve off (broke one screw off in the process ) and this is what that looked like:

Clean it with carb cleaner and clean out the recessed area in the TB where the pintle seals.

Yes carbon city,and carb cleaner does work well, I used a tooth brush to scrub the pintle.
Here is the IAC cleaning link: https://www.gmforum.com/normal-maint...2/#post1597076

Thanks for all of the information. She cleaned the IAC, ordered a new MAF, and also replaced the PCV valve (no telling if that was the original or not). As soon as she gives me some updates, I’ll be sure to pass them on here. Thanks again!

Sis got her new MAF delivered today. She installed it, put the cleaned IAC back on, replaced the PCV valve cranked it and drove it a little ways tonight and so far so good. Tomorrow she’* going to give it * good test drive after she goes to the parts house and get her codes cleared out and reset to see if any new codes come up. I’ll keep y’all posted. Thanks again for all the tips and advice.