Chris DeNigris

Hi Guys,

I need a little help diagnosing an issue with my v6 convertible.

My car is having an issue after driving that when I put it in part the RPM's just drop out from around 700 to 500 really fast. They then jump right back up to 700 and resume normal idle after a quick studder in the engine. A few times recently however after putting the car in park it has literally just cut the power completely. While this doesn't happen often it has happened on at least 5 occasions in the last 3 months. I brought it to my mechanic and asked about the idle air control valve. I don't even know that this car has one like previous mustangs? Maybe you guys can clarify that one, or is it the MAF? Is my throttle body bad? I had my spark plugs replaced recently. I also went from 2.73 gears to 3.55 gears but the problem existed before and after the gear upgrade and that should not be related. I've read that it could be a vacuum leak but the car runs completely normal while driving until I put it in park and again it is a problem that is inconsistent.

There is no check engine light on. My mechanic checked this 2 months ago and said there were no codes at all and he thoroughly tested it for me.

One other thing. I am using a pedal commander for throttle sensitivity. I don't think that should cause a problem but you never know I guess. I'm not sure if I had this problem before I started using that but seems more like a hardware issue to me.

Any help is appreciated. Looking forward to your responses.

Thanks.

Derf00

What do you think Pedal Commander is? It's a piece of hardware (with electronics in it).

I would start by removing it to see if the problem goes away. If it does then you found your problem. If not. Leave it out until you figure the problem out.

If removing it doesn't fix it, a lot of times the throttle body butterfly is gummed up and needs a thorough cleaning, especially around the outer edge where it comes in contact with the throttle body itself. The TB butterfly is commanded to open a certain amount (%) based on what position the pedal is at. Idle only has a fixed range so once it's opened all the way for idle, it doesn't have any more room to compensate for idle issues. Thus the most likely reason it started as an occasional thing of dipping the idle and progressively got worse to where it can cut out.

Use only TB or MAF cleaner. If you use something too harsh it can mess up the brass colored finish on the butterfly which has some sort of purpose.