Idle surging in traffic after engine is hot.

[Liam Wulf]

Hey there. I have a 99 Civic LX manual transmission. It has about 180K miles. It does this infuriating thing where, if I'm driving in stop and go traffic, the idle will slowly begin to mess up. normally it idles at about 800 RPM, according to the tach. It'll start idling higher, sometimes upwards of 3000 RPM, and it goes up and down 1000 RPM or so. If traffic clears and I can run it at speed for 15 minutes or so, the issue goes away. I have tried replacing the idle air control valve on the throttle body, but the new valve made the car idle at 1200 to 1500 RPM consistently. Ended up putting the original IACV back on the car. My mechanic says I should find a used throttle body to put on the car to test if it's maybe the throttle body itself. I'm wondering if there's an air bubble in my coolant that's getting stuck in the IACV during stop and go traffic that's causing it to go crazy. I've checked the coolant levels in the radiator and those are fine. Car never overheats. The car had been sitting for almost 2 years when it was purchased from a family friend. The car is throwing 2 codes, 1 for the IACV and 1 for the crankshaft position sensor, which I believe is in the distributor. I've been looking for a replacement distributor at a decent price, but... those seem to be made of fairy dust, and finding a used throttle body for a MT civic is like picking hen's teeth. I'm a disabled vet trying to keep this thing on the road without spending a fortune. Any help you all can give would be greatly appreciated. Thank you