Pontiac Repair: Engine Idling, pontiac grand prix, vacuum leak

Question
I have a 1999 Pontiac Grand Prix, 3.1 V6. It has been running rough for a short time, and now will not stay running without pushing the accelerator. However, when you do push the accelerator, the engine accelerates to about 3500 rpm and remains there for a few seconds after releasing the pedal before idling down. It makes no difference how far you push the pedal down. You can't really get the pedal in the right position to keep it running at around 900-1000 rpm, unless the car is in drive. Then it is possible to keep one foot on the brake, and a little pressure on the accelerator and it will run as you think it should. Where do I start? Thanks.

Answer
Hi Mike:
When it is running does it seem like is running on all 6 cylinders or does it misfire? If it runs smoothly but races I would look for a Vacuum leak. If not vacuum leak is found then I would try running the car with the MAF sensor unplugged and see what happens it may not race but it will hesitate. If that doesn't work then try the same thing with the TPS. you should have the same result. What ever sensor of the 2 you unplug and the engine runs at a normal isle speed is where I would start looking for an issue either with the sneor or the wiring to the ssnsor. Before this started happening did the service engine soon lamp come on? If so do not unplug anything and if you can drive it to one of the big box car parts stores let them scan the car for codes and see what codes ate stored that is a starting point. by unplugging the sneors and running the car will set even more codes and you will be chasing your tail. Good luck :)