Engine revs when clutch is disengaged

Hey all, I have a 90 Eddie Bauer Bronco. It is 5 speed and I recently installed a hydraulic clutch. For the past few months I've had a really wierd problem where my engine would sometimes rev an extra 1-2,000 rpms when I disengaged my clutch to shift. I thought maybe the trottle cable was gettin hung but i followed it and messed around with my throttle body and that didn't fix anything. I also changed my throttle control sensor recently thinking I finally figured out the problem but that actually didn't fix it either. It doesn't happen every time but about 60-70% of the time. When it revs it doesn't matter if I let out the clutch again or pump it. It normally just hangs untill I shift or if I wait for it to come back down it takes about 20-30 seconds. I'm really stumped on this one. I was just wondering if anyone else had had this problem or heard of it before. Any speculation on the problem would be amazing. Thanks guys

-Dave

For anyone with the same hang: when the revs stay up for 20 or 30 seconds after you clutch in, the idle air bypass valve on the throttle body is the usual cause. It gets gummy with carbon and sticks partly open, and the computer takes a while to pull the idle back down. A vacuum leak or a throttle that doesn't fully close can cause the same thing.

Clean the throttle body and the bypass valve with throttle body cleaner, check that the throttle plate closes all the way with the cable disconnected, and look for split vacuum hoses. Since the TPS was replaced, also check its voltage at closed throttle, because a misadjusted one can make the computer think you're still on the gas.

Our 1987-1991 Bronco schematics page has a cutaway of the Bronco idle air bypass solenoid showing how it meters air around the throttle:
https://www.supermotors.net/reference/ford/bronco/1987-1991/schematics

Dana