I have a 99 gsr...the car will start and idle with a bit off surging on the cold start as it warm up the idle comes down levels out around 700-900 rpm then out of no where it falls on its face almost stalling out it will recover surge up to about 1000-1200 rpm the return back to around the stock idle. After it warms up and gets up to temp I unplug the iac and it dies immediately plug it back in starts right back up...from what I understand the car should idle on it's own w/out the iac plugged in at around 500 rpm on the ecu. It will drive but stalls when I take it out of gear coming to a stop as well ...

 

Try replacing the IACV, and check the wires going into the plug.

 

did this just start happening out of nowhere? any mods?