High idleing after putting foot down. Someone seen this before?

[Ike]

Looks like I have a CIS problem with my 1983 GTI Cab.  People say they know someone who had a similar problem but cant remember how they fixed it so hopefully someone can help.

The car runs smoothly until I stick my foot down and drive at above 4000 revs. Almost every time the revs then idle at about 2000 or higher for anything up to a week (of low rev driving).  It does correct itself but its im worrried that other things will occur from the issue.  It seems to be over heating too although the dash board thermostat is not working.

Anybody could an idea of were to start looking.  Im new to GTIs and and the CIS injection system.

[GemGTI]

Check that the idle screw hasn't come loose. I had a similar problem but was the other way round, my revs dropped so was idleing at 600rpm and would then cut out. Bacically the idle screw was loose so any vibrations would cause the screw to move, therefore adjusting the revs. Hope that makes sense, Gem

[SpearMintTom]

Same happened with me, also make sure you're throttle cable isn't obstructed by anything or tied down

[Ike]

Thanks for the replies. Unfortunately its not either of those things, wish it was though.  Think Im going to try checking the throttle switch and if not that then checking whether the throttle valves can close, might need a clean.