RPM goes to slow back to stationary

[Audi80/90ClubEurope]

Hello you all!
My Audi has a technical problem since a week.
It did not went back in rpm. Even if i dropped the clutch it stayed on the last used rpm.
Replaced the temperaturesensor & placed another ISV.
It goes back in rpm now but slow to 1200.
If i disconnect the temperaturesensoror the ISV it goes to 800-850.
Looked at the hoses, i had some broken ones, replaced them but no differnce

What can be the problem? It is a '86 Audi 90 2.2 KV

[mike74]

Does it have the throttle damper fitted to it? Could be a bit stiff?

[Audi80/90ClubEurope]

i started it up again today, it was better but didn't go lower than 1200. When the engine was running and i wasn't giving gas or something it went back in rpm really fast to 850 and went back to 1200.