On my 06 Ram MegaCab (automatic) if i rev it up and let off the throttle it stays revved for quite a long while (at least 3 seconds) before idling down... Maybe its normal but i really dont like it.

 

This is normal. Your engine is computer controlled (i.e. throttle by wire). Most vehicles nowadays do this same thing.

I can think of several reasons why your turbo diesel stays revved up for a few seconds,

1. the turbo spools up a bit and continues to force air into the manifold after you take your foot off the accelerator pedal. The computer has to fuel to match to prevent lean conditions and possibly for emissions control (I'm not certain of that).

2. many new cars that are throttle by wire also reduce throttle input to a minimal level, but not zero, after you take your foot off the throttle. My '07 Legacy GT will hold partial throttle for approx. 10 seconds, this may be part of a drive train life improvement process. Simply put if you are on and off your throttle a bunch your drivetrain sees a lot of shock loading, however if the computer eases on and off the power output (by throttle control) the drivetrain sees less abuse or shock loading.

 

If it idles down smoothly, no problems. If it hesitates on the way down or acts like your foot is slightly hitting the throttle then you have an issue.

 

Some of it also comes from built up rail pressure at the injectors.

 

It might be just me, but I've noticed it only does it on autos. On my 05 it always did that when I revved it. On my 07 with the g56, it doesn't do it, idles right back down. That could be cause of the turbo spooling thing though. Also, I can make my standard smoke by revving it in neutral by barely tapping the throttle. On autos its alot harder. I couldn't hardly get my 05 to smoke at all in neutral, on my gfs truck with bigger injectors, and twins, it'll smoke pretty good, but only if you get on it hard, then it hangs, and takes a while to idle back down. differences in autos and manuals is part of it I guess

 

What would the issue be if it idles down rough?...I have the same problem