It's it normal when revving the car high that it slowly comes back down to normal limit. I notice it happen twice but not every time random. Also I have a custom exhaust system.

 

If i had to tke a guess its probably back pressure doing that !

 

I don't understand what your saying

 

agreed

 

I had the same issue before. When your at idle and reving to 5 or 6 rpm then the rpm's fall down very slow. I find that a little weird also anyone else had this?

 

Happens in my car too, I think its fine.

 

Mine does this as well. You shouldn't be to concerned since we are all experiencing the same. In my old 2003 Mustang GT 5spd. It did the same thing. I figured that the slower the rpm falls the better its clearing out the combustion in the engine and clearing out the exhaust into the manifolds. I'm no engineer so please don't blast me for my guess.

 

How slow is slow. I just did mine, 5000 rpm to idle was less than a second. That's pretty quick for me.

 

I would check the tps sensor. I know it's a 7th gen but I had that problem on my 5th. Reved high out of no where then it came back to normal.

 

Mine is the same way, I notice it more on the highway and back roads in sport mode, I think the computer is preparing for you to get back on the throttle hard so it keeps it in an optimal RPM range to get your moving again. (Wasn't sure if you were talking about idling in neutral then revving or when the car is motion.)