Fluctuating idle in warm weather - '95 Begi S1
 

On days above 60F my car will start to have a fluctuating idle after the car is warmed up and I have driven it a little bit. The idle will jump from ~1,200 to ~1,800 and back down repeatedly. Sometimes it will drop down to a reasonable idle sometimes it drops to ~1,100 and stays there. This is not affected by the AC, depressing the brakes, or anything like that. When it is below 60F outside this problem doesn't seem to happen at all but the warmer it is the worse the problem. Yesterday it was 90F or so and the engine was violently bucking when the idle was fluctuating.

I have checked for vac leaks and have found none. When the car is idling properly I get about 18 in. vac. I have replaced the PCV, and IACV. During the IACV install I noticed a good 2-3mm of black gunk on everything behind the TB flap. I cleaned as much of it as possible off the TB and some behind it.

Any ideas on what else might be the culprit? IAT, TPS, RRFPR, O2 sensor?

Edit: This has been happening for a while now and I don't think it corresponded with the turbo install I did a while ago or any maintenance I have done.

Also here is a video of the idle problem but in this video the idle fluctuations are a bit more tame than they can be.