car won't rev smoothly

[catch]

I’ve got an issue with smooth revving on my 16v k-jet.
When I rev the car above 3000rpm and then let go of the gas the revs seem to stick at 1800, jump back up a little for a moment then drop back to a smooth idle.

I’ve checked the cable and that seems to be ok

Any ideas?

[RickyC]

check plugs, leads etc first,

[golf8v]

plug and leads not likely to affect idle. most coming problem would be idle air control valve..

[catch]

The plugs are 3 months old and the leads are all clean. The car runs perfectly apart from this.
I have cleaned out the isv and it buzzes when the ignition is on. Could it be the throttle valve switch? I've seen it in the Haynes manual but not sure what it does exactly...

[RickyC]

plug and leads not likely to affect idle. most coming problem would be idle air control valve..

yeah my bad, read it too quickly, check the idle control valve as said previously

[catch]

Ok. thanks.  I'll unplug the ISV and see if the car revs smoothly.
If it does, how do i know if the problem is with the ISV itself or the controller behind the centre console?

Is there a test for this?

[Gambit]

check the throttle closed switch is working correctly

[Mk1Mad J - 16v]

The over-run cut-off valve should be doing something when you let of the throttle, maybe it isnt doing what it should 

[catch]

I tested the throttle valve switch with a multi meter as per the Haynes manual. All readings are fine and you can hear the switch click on and off. I cleaned out the throttle body although this was pretty clean to begin with. I tested the revs when the isv was disconnected and the problem is still there so I don't think its that.

This leaves me thinking its the the overrun cut-off valve.
Has anybody ever cleaned one of these things? Is it actually possible to clean it or is it a sealed unit?

[Mk1Mad J - 16v]

Will check my manual when I get home, there should be a vacume line on the over-run valve too, is that missing or damaged?