After I rev or even touch the throttle it will stay at that rpm for several seconds before it drops back down. If i disconnect the vacuum line going to the IAC from the intake it (just on the intake side) it will act almost normal, just idles high. Already tried replacing the IAC. The car has comp cams 262s, 75mm throttle body and plenum, and headers. From what I've read none of these require a tune though. Did all of these at once and had the engine out so im not sure if these are causing...

RPMs hang for seconds before dropping