Yes, the Idle Control Valve has moving parts (I just cleaned mine - very easy - check the DIY here)!
I don't know too much about the tech details (despite the fact that I own a 91 C2
, but it sounds to me like a fuel supply problem. I had such problems on other cars and it showed the same symptoms. What happens if you suddenly accelerate on the freeway - loss of power would confirm my suspicion?
Good luck!