revving when push in clutch

[supradrift]

I was wondering if anybody has ever had or heard of the problem when i am driving and i go to shift when i push in the clutch the car will rev up about another 500 rpms and slowly rev down. It mainly happens when the car is cold but it still sometimes will do it after it warms up. If when it starts revving up and i snap the throttle real quick it will idle back down normal. Any suggestions???


'87 turbo
3"downpipe
highflow cat
3"magnaflow catback
boostcontroller