My revs keep dropping.

[mark1gls]

My tick over keeps dropping down to 500rpm every now and then, It starts fine and drives alright but every now and then the revs drop down on tick over. I have had a look for an air leak found one then replaced the hose at fault but its still playing up.

I have pulled of the electric connection on the (I think its the AAV? the black thing on the drivers side strut with two pipes running to it and its getting power)
and sometimes when I plug the power back in it ticks over fine but not always. VW call it "solenoid change-over valve" 026 906 283B
Could this be at fault or am I looking in the wrong place.

Its for an DX fuel injection engine.

[PeteGLi]

I have pulled of the electric connection on the (I think its the AAV? the black thing on the drivers side strut with two pipes running to it and its getting power)
and sometimes when I plug the power back in it ticks over fine but not always. VW call it "solenoid change-over valve" 026 906 283B

That is the idle control valve and it has a control relay marked either 1 or 57 on top of the fusebox. It is designed to smooth out the idle when heavy loads are switched on.

The AAV - auxiliary air valve is situated under the manifolds on the rear of the engine on the driver's side of the car.

[mark1gls]

Well I think I have now fixed the car, what happend is the idle adjustment screw had worked itself lose, I could turn it with my finger! I guess the idle control valve was keeping the revs up most of the time but not all the time. I took the screw out carefully as I did not want to drop it on the drive as its now easy to get to, gave it a clean as it was black and put a small drop of thread lock and screwed it back in and reset the idle.

At least it was not the idle control valve as they are £50 + VAT from VAG.