Another day, another question about the issues with the project car :D
To try and simplify the behaviour: when the car is cold and it starts, it runs and RPMs normally; the RPM is a bit over 1000, I assume it's some kind of cold-start mechanism.
Once the engine is warm, it has trouble maintaining the idle. When I'm stopped and the car is in neutral / or I'm holding the clutch down, the RPM starts dropping as if it's about to stall, then it catches itself and goes back up. After that, it starts oscillating up and down.
In the video, I'm not touching the throttle at first. You can see the RPM drop, recover, and then fluctuate. Near the end, I give it some throttle, and when I let off, the RPM drops all the way to zero and the engine stalls.
It seems to happen mainly/only when the engine is warm. If I keep giving it a little throttle, I can keep it running, but it's happening more often recently, and it's very hard to keep it from shutting down every 30 seconds in high-traffic situations. Until a few weeks ago, it would lose RPM but not turn off, and it would pick up the RPMs and even stabilize itself occasionally.
I would appreciate any pointers on where to look or what to look for.