My friend's 94 GSR....at idle the car is bouncing between 1000 and 2000 rpms and I disconnected the IAC and it was varying +-50 rpm but you could still hear the revving. Is there something other than the IAC that could cause this? Maybe an intake manifold leak? Is there a sensor that controls the IAC? I couldn't find anything that looked obvious after removing the IAC, thanks.

 

I had a similiar problem with my B20. Ended up being the intake manifold gasket.

 

Take off the intake. Turn on the car and stick your finger on the hole on the left side of the TB while the car is running. If the motor sputters and almost dies, replace your Fast Idle Thermo Valve. It is located under the TB. The bolt may have just come loose, so thats the first thing to check on the valve.