2006 Mustang GT, 90,000 miles, stock, auto,recently on on start up after engine is off for several hours it idle's smooth, once in drive I travel aprox 600 feet to a stop sign, as I am slowing down the engine surges form 600 to 1500 rpm, repeatedly , once I come to a "complete" stop the engine runs smooth again and the problem will not repeat until engine is off for several hours. Anyone have a clue what is causing this. Other than the above problem the engine runs perfectly.

 

Maybe a Throttle Position Sensor going bad?

 

Always try the simple stuff first: Clean the TB, clean the MAF, replace the fuel filter, run a tank or 2 of SeaFoam. Then go from there.

 

Hey Nuke, quick question for you. I might be reading into this (given your screen name and location), but do you work at Grand Gulf?

Also I second your opinion, def try the free/cheap fixes first.

 

Try cleaning the Throttle Body but I have had this issue for years and no dealer or repair shop can diagnose it. It really comes and goes as it pleases. If you clean your TB and still have the problem try to take note if it only happens or happens worse with your A/C on because I have read something about our ac compressors causing some kind of issue with the idle but I never read into it any further.

 

Definitely try the easy stuff considering the mileage. Also if it is modded, most times it is in the tune. It took me multiple tunes to correct my hunting idle. Would start up fine and idle great until I took off and came to a stop sign. Then it would hunt. This is pretty common with our cars.

 

Thanks for the suggestions, I plan to clean the TB first, and some other things you all suggested to try to fix the problem. Thanks again ,