'04 NB2 idle issues

[HarryB]

Now my idle issues got back, even worse this time. Approximately 2 months back, I had the car idling low and sometimes stalling with "external" load while idling (headlights on, turning the wheel). Back then I removed the intake tube, sprayed the ICV with brake cleaner and blasted with compressed air, disassembled the EGR actuator and lubed up the spring, and did a base idle set, which seemingly worked. However, the issues got back a week or so ago. I would normally believe it is the ICV again, but the interval seems too small for me to justify it. Symptoms:

Car idle is usually OK, but sometimes it is too low (650-700rpm), which causes engine stall. If I rev it up by throttle blipping, it goes back to normal idle (850ish). Strange thing is that sometimes, when stopping in traffic lights, it idles too high (1000ish) without any obvious reason. These two modes can happen back to back (from one traffic light to next). When idle sits high, if I blip the throttle, there's a slight hesitation in the RPM drop below 1500ish.

Also, when driving and decelerating, car in gear, sometimes it bogs when revs are below 2000 RPM. Seems like some sort of "clutch judder" or "hiccups". If I press the clutch and rev it up, it goes away.

The thing that drives me crazy, is that there's no consistency. All these things happen randomly, and sometimes not at all during my daily commute (approx. 8 km).

Ideas:
ICV
Loose ground point or connection
Bad spark plugs (will change them today)
Faulty RPM signal to ECU (cam sensor?)
Vacuum leak (PCV)? Not quite likely IMO because symptoms would be consistent.
COPS/Wiring issues?

Any other leads? This is literally driving me crazy...