B230 Engine 740GL manual saloon, pierburg b25 carb. Following instructions in FAQ, I took off the carb, cleaned everything thoroughly, replaced gaskets, inspected throttle linkage and all that stuff including vacumn hoses.

Installed new fuel pump, new hot start valve, new idle air control valve, new fuel filter. Sure the car idles great, but when car is warmed up and I come off the highway the idle has shot up to 1500 revs. I have to smack the gas pedal to bring down the revs to normal.

I sprayed carb cleaner all around the outside of carb. Spraying between the semi-automatic choke and the carb the idle shoots up for a minute or so. I guess because the spray has evaporated. But I can't understand this. Any clues? The only thing I could see is a thing cam, I don't know its function and what it should be set to. I know its not the throttle cable because I tested it by disconnecting the link rod and the problem is still there.

Also, the 3 screws that secures the choke housing have become loose and I can't tighten them as the threads on the plate are worn through. Could this be connected to the problem?

Thanks in advance.