Air leak problem?

[Maltloaf]

Hi Guys,
The old 8v digi woes have struck again.
I believe I have an air leak somewhere and I hoping someone might have encountered this before.

When the engine is up to temp I sometimes come up to a junction the revs are slightly higher than normal (1200+) at idle. If I lift the clutch slightly with the brakes on I put load on the engine it drops back down again. Almost like the vacuum is pulling something shut.

I have disconnected the ISV and have exactly the same problem, so I do not think it has anything to do with the blue temp sensor or ISV, but I have only disconnected the connection from the ISV and not removed its plumbing from the idle circuit this will probably be my next course of action.

I have sprayed carb clearer over some of the joints on the inlet manifold while the engine is running but has not given any signs that there is anything leaking.

Could it have something to do with the dizzy advancing the idle? The MPG is quite bad when the car does this.

Any ideas?
Cheers
Matt

[rubjonny]

check the idle switchunderneath the throttle body clicks when throttle shut, and the wiring tothe throttle body hasnt snapped

[Maltloaf]

Both the throttle switches click in the correct positions and were working okay when I tested them a couple of weeks ago, but TBH I have not tested when it is hot. 
I am thinking it is around the throttle area. Is there any tolerances I can check or adjustment I can make to the throttle or is this best left to a VW Tech? The engine has done 160k so there might be a little slack in this area.
Cheers

[rubjonny]

main thing is that it closes to the throttle stop firmly. if this is ok then dont fiddle with it! usually if it doesnt hit the stop eather the throttle cable is too tight or the idle switch is adjusted too far out.  another spot for problems is the idle screw, if the oring is worn it will leak airt and sometimes unwind itself!

the breather valve is a good spot for leaks too, check the rubber bung hasnt split and the breather valve sits in it firmly

[Maltloaf]

Cheers I will check this.

[sleeper16]

my abf was doing this, might not be of any help but try disconnecting your air inlet and putting your hand over the throttle body this should make no-little diffrence at idle as it idle mainly off the isv but if it makes a big diffrence like mine did you know you have an air leak past the butterfly.

mine did this at all temps though so probably not the issue just thought id mention it

[Maltloaf]

This might work but I would have thought that there would still be air passing via the idle screw. It will certianly allow me to check the throttle butterfly and elimiate a few things. Cheers

[rubjonny]

wont work on a digi as if you do that the afm wont be working and so the ecu wont know how much air is flowing

[indigti3]

maltloaf, can you hear what seems to be a kind of whistling under the hood every now and again whilst your driving?

[Maltloaf]

I haven't noticed any odd whistling noises.