Engine: Blacktop 20v

Has anyone encountered 'lingering revs', where after you lift off the accelerator pedal, the engine's revs will hang there, or even increase a couple of 100?

I tried playing around with the dashpot/throttle opener clearance. If set to spec, the revs hang up high, if disconnected completely, the revs hang down low. Quite annoying when changing gears, cause the revs are way too high for the next gear. Makes for easy downshifts though, I guess?