[Bearintheair]

Old thread I know, but I came across this while searching for the solution to the exact same problem and I've managed to solve it, at least for me and hoping I can at least guide someone. Symptoms were the same including a magneti marelli throttle that seemed to be healthy.

Started by cleaning the throttle body, as it was filthy and sticking open occasionally, so that helped a little but didn't solve it. What solved it for me was replacing the thermostat (and rad hoses but I doubt those did it).

Noticed in the summer it would run slightly cool sometimes, but didn't think anything of it. As temperatures dropped in to winter the engine temp was getting lower and the heater was getting poorer so I decided it was time to replace the thermostat. This seemed to solve it, and even after a battery swap (which makes the throttle relearn its mappings), I had a few moments of funky idle as it learned its self, and it's been perfect since.

Hope this helps someone.