knirk

I have a tricky problem with my car that I can't seem to solve.
The car is a is a 91 with 305 TPI and T5 gearbox.
The problem I have is that I can not get the idle rpm to sink below 1200 rpm as long as the car is rolling.
No matter what speed I have when I press down the clutch, the rpm does not want to drop below 1200.
When I stop completely, the rpm drops to normal idle.
The problem is intermittent, so sometimes it drops to normal idle when I press down the clutch.

I have tried to log the car to find something, but every time I tested that , the car works as it should, ie rpm drops to normal idle.
Have changed both TPS and IAC, cleaned throttle body and adjusted the throttle body so that the IAC counts are OK and ignition i set to proper value.
I've checked the PROM, i'ts AXXC which I believe is the correct one for a 305 w T5

Now I'm running out of ideas about where to look for the error.
Is there any one who knows and can elaborate on how and if the VSS signal in some way affects the IAC, have anyone else has encountered the same problem and found a solution for it.
I have no reason to suspect that the is anything wrong with the VSS signal since the speedometer is working.
But something tells me that the IAC in some way is controlled by the VSS.