Engine stays revved up after releasing gas pedal, slow return to idle

[theirongiant]

I've got a 1993 525i, M50 engine, with 195k on the clock that I just acquired from a third party. As far as I know, this car has been well-taken care of, and driven by a woman the whole time. But she never pushed the car close to redline, or she would have noticed that the engine stays revved up for a long time even after I've clutched and shifted out of gear. If I stay in neutral and watch the RPMs, they take a while to drop back to idle.

The problem, of course, is that the engine could sit near redline for too long, and it also makes for rougher shifts.

This happens about 90% of the time, even if the A/C is turned off (which my old car used to do only when the A/C was turned on). On rare occasions, the engine will actually accelerate after letting up on the throttle.

What's going on with the car? Stuck throttle body? Something else? Easy fix? Expensive if taken to shop? Tell me more, please. I've driven a 1991 325i before this car, and I'm comfortable doing some maintenance if given the right tools.

[632 Regal]

check for vacumm leaks, check and clean the ICV. Does the car have any stored codes?