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Ron
Ron, ASE Certified Technician
Category: Pontiac
Satisfied Customers: 35857
Experience:  34 years as a Tech
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2003 Pontiac Grand Prix 3.1 L. After the car is warm the

Customer Question

2003 Pontiac Grand Prix 3.1 L. After the car is warm the RPMs go from 850 to 1800. Then when you are going down the road, without putting your foot on the accelerator, the car keeps gaining speed. You have to ride the brake all the time. Yesterday the RPMs reached 3500 while sitting in a parking lot in park. There is no check engine light coming on at all, so no trouble codes to read.
Submitted: 2 years ago.
Category: Pontiac
Expert:  Ron replied 2 years ago.
Hello, my name is ***** ***** I am a professional here at Just Answer. I have noticed that your question was not getting a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.
The type of problem you are having can be caused by either a sticking IAC (idle air control valve or a failing Throttle position sensor. I would start first with cleaning the IAC and if the problem returns then test the TP sensor to see if it is failing. See steps to do so in the link below.
https://dl.dropboxusercontent.com/u/104923897/TP%20Aug%205.pdf
Customer: replied 2 years ago.
I have ordered both of the parts you specified on Amazon. As soon as they are installed, I will rate your service. They should be delivered on Friday.
Expert:  Ron replied 2 years ago.

I would consider cleaning the IAC first before you replace it. When replacing any of theses be sure to disconnect the negative battery cable before doing so as well. I'm here if you need me.

Customer: replied 2 years ago.
tonight I changed the IAC and drove it and there was no difference. It was however all cruded up. Then I changed the TP sensor with no change. I disconnected the negative battery cable for both changes. After I changed both sensors I drove it on the highway and it kept gaining speed from 30 to 55 by itself without pushing on the accelerator. Finally i let it run in the driveway and the idle kept getting higher as the engine got warmer until I finally shut it off. The exhaust had a bad sulfur smell. What next?
Expert:  Ron replied 2 years ago.
Has the computer been scanned and if so are there any fault codes setting?