I have a 1999 Grand Prix GT with a 3800 series 2 motor. When the temp reaches between 195 to 210 at idel it will flutter or cough, and about 1 out of every 10 of those flutters or coughs it will die. I have tried what I believe is to be just about everything, but am looking for help in solving this problem. Knowing my luck it is probably something simple that's being overlooked! Can anyone Help?

Try cleaning/replacing the Idle Air Control Valve. Also, remove air intake--then, clean the throttle plate, throttle body, and upper and lower ports. Afterwards, clean the air box with a damp cloth and replace the air filter.

Ensure the platinum spark plugs (ACDelco only) have been replaced in the last 50,000 miles. If the problem persists, replace the Ignition Control Module (ICM) and coil packs. I recommend replacing these problematic components every 120,000 miles or 10 years, whichever comes first. ICMs are notorious for breaking down under heat.

You might have an air or a vacuum leak. This is very common. Open the hood and listen for a hissing sound when the engine is running.
Un-regulated air can enter the engine through:

• a vacuum leak
• a dirty airflow sensor that is not reading airflow accurately
• an EGR valve is not closing and is leaking exhaust into the intake manifold
• an EGR valve that is allowing too much flow.

If it is hard to pinpoint use a spray like WD-40 around the intake manifold and vacuum lines and see if the engine stumbles or if the idle is affected. Be extremely careful when doing this!

Also, your throttle body may be carbonized and needs to be cleaned. This can cause all sorts of idle and hesitation problems. This is caused by the throttle plate not seating properly. The First thing I would do is clean out the throttle body with some throttle plate and intake cleaner and a small brush. Another common cause would be the Idle Air Control motor. This is very common on older cars.
The IAC motor gets lazy and can't keep up with the fast idle changes. Also when the IAC motor is out, check the passages for carbon build up. If they are plugged they need to be cleaned out.

Thanks Guys! But I have cleaned the throtle body. Checked for vacuum leaks, replaced all sensors with new. I will try the spark plugs though. I have NKG plus in it now. I was told that it needs updating in the computer. Is this true or is this someone just yanking my chain? Thanks Again for all your help! :o) :)

Personally, I would only use the exact ACDelco plugs that came in the engine. After that, move on to the ICM.

On some cars, cleaning the IACV doesn't work--only replacement solves the problem.

Are NGK Plus single or double platinum plugs? I've never heard of NGK Plus. The new plugs could easily be the wrong heat range--ECMs can be pretty particular.

Not for sure! Sorry
:confused:

Do you mean NGK plugs, not plus?
The ECM may well have updates available but you have numerous systems that need tested before replacing.
Your throttle position sensor may not be reading correctly and the ECM cannot know good info from bad, therefore cannot make the proper adjustments. What sensors in particular did you have replaced and by whom?

Thank You for all your help! Now for the fun part! I thought that I would let you know that I did get this issue fixed. Don't Laugh too hard now... it was just a simple matter of grounding 2 wires to the tranny. They were overlooked when putting the motor in. Thanks again!

That's wonderful! and you have the assurance of having the other maintenance done also. Glad to be of assistance...

K