Originally Posted by Built_not_bought
Does it start doing it after the car warms up? If so, you have a faulty IACV or the wiring. You mentioned that the IACV had already been replaced. I've been on the same boat where the IACV that I purchased used was also bad, and the problem persisted until I installed a brand new IACV. Also, I had a similar issue about 20 years ago with my 96 GSR. Actual ECU was the culprit at that time.
It’s a brand new IACV. Straight out of the box. The surging, however, happens no matter what. Start the engine and it will idle high for maybe 10-30 seconds and then start surging. Drive normal and it’s fine. Take it out of gear and it will keep surging. When I unplug the IACV while it’s warmer then it will just die. I went ahead got a new throttle position sensor and installed it today and cleaned the whole throttle body as well as getting a new gasket (found out old gasket is absolutely f****d lol). I haven’t bolted it up yet but I’m hoping it will help. I keep getting told there might be a bad leak. Next is either the intake or exhaust manifold gasket because one of those might be bad as well, probably both