Thread: P0171 and running rough

Hey guys, not sure if this is the right spot to be posting, its only my second post on here.

So lately I have been having some issues with my car, it really idles like crap. Drives fine until on the freeway and cruising at 2000 rpm, the rpms start bouncing, I speed up and that goes away.
Yesterday I got a P0171 code that popped up for about an hour of driving, the code came out of no where, and disapeared.



Here is the data from the P0171

One thing that I have noticed is that my cars idle gets a hell of a lot better if I throw it in neutral or in park. It also runs better with the AC on.
It almost sounds like my engine is tapping the frame. Could this be a motor mount gone bad? I really not sure whats going on over here.


Here is what I have done in the last seven months, most very recent.

MAF Sensor (threw code, replaced) 7mos.
LIM Gaskets 7 mos.
IAC (very dirty, replaced) 7mos.
New Plugs 1mo.
Wires 1mo.
Coil Packs 6mos.
Temp Sensor 2 weeks

Sorry for the lack of info here, most of the time I have no idea whats going on.


2000 GTP Supercharged, no mods. 199,000 miles on it.

Thanks in advance for any advice!

Awesome! Thanks for the suggestions. I don't have a smoke tester, is there an alternate way of doing this with like a cigarette or something? Also, I took a can of carb cleaner and sprayed it around all the hoses and the intake, no change in idle.

I did have my brother do the gaskets for me, when I had them done, do you think that he could have done them wrong or is this possibly a head gasket issue? I'm not loosing any coolant and there is no oil the water.

The code is gone and has not come back, but the car still has a rough idle and shakes pretty bad at start up for about 5-10 seconds.


Thanks again!