Odd rev hang

My GTi has developed some interest rev hang, more noticeable when cold but happens when warm too.
The car will idle okay, slightly higher than normal, but if you blip the throttle it will occasionally stick at 1500 RPM and idle smoothly there. If you then "pull" the revs back down to idle by holding it on the brake and letting the clutch it'll go back to the normal RPM.

I've tried unplugging the ISV while this is happening and the revs obviously fall, but as soon as its plugged back in they jump back up to 1500.
I've also tried unplugged in the the idle switch and that doesn't make any difference either

 

Mine was doing that, and on a suggestion from @rubjonny esq, I looked at the throttle cable. Which was fraying, and sticking.

Now admittedly, it didn't solve it 100%, (also had a faulty AFM) but it was definitely partly to blame.

 

Cheers! I did check that and the throttle is closed fully it would seem while this happening. I'll try swapping the AFM with a spare and see if that helps

 

Throttle pedal pivot points were sticking on the green golf last year, bit of lube sorted the problem.

 

I'll go and check again but I *think* pressing the WOT switch made no difference. I'll get the multimeter out later and check there is actually voltage on the plug

 

Some progress? Gone round hitting stuff and moving wires while the events were happing to no avail. If it creep up the revs to about 1500 then let go it'll do the hanging 95% of the time, if I rev it hard then it fall it'll only 50% of the time. Unplugging the the WOT switch either has no affect or makes the rev really shoot up. I've checked the throttle screw and that hasn't moved, still has paint on it. Could it be the FPR?

 

Have you any air leaks - vac lines all still securely attached?

I have a similar issue i think - idle is 1500 cold, 1200 warm. Can't get it any lower unless i unplug ISV and in which case it drops to 950. My microswitch on the throttle body does nothing when pressed manually whilst throttle is open. My revs don't hang from say 4000 - they immediately drop down but only to 1200/1500.

If plug back in my ISV the idle remains at 950 whilst running. Switch it off again the revs are back to 1200. I've not solved mine sadly and have given up for a bit as plan to take the car for a rolling road set up at Stealth at some point.

 

Assuming this is an 8v digi the idle issue often seems to be a combination of a few things. Check air flow sensor, ISV, and all vac lines for leaks. Further to this, I found cleaning inside the throttle body made a huge difference. The small butterfly in particular was caked in old oil from the breather pipe. Blasted it with throttle body / carb cleaner and made a huge improvement.

 

Still no idea on this, checked for vac leaks and there are none. I have a spare AFM so I'll try that. I had my throttle body off a few months ago and cleaned it then so I doubt its that. If the car had a mechanical distributor I'd say it was like, like getting stuck slightly advanced. 8V digi dizzy's are just a straight through shaft with no mechanical advance if I'm correct? I'd already tried running with ISV unplugged and it does the same thing so its not that.

 

Well brought the car out from hibernation yesterday, don't have the spare AFM with me but I've rechecked and no Vac leaks. If I quickly blip the throttle I can get it to hang at higher revs every time, a longer blip of throttle clears the fault and the car falls back to idle. If I unplug the throttle position switch, the revs start to climb, as soon as I plug it back in they fall back down to the "raised" idle. Again in these situations, the same fault occurs regardless of if the ISV is plugged in or not. Unplugging the temperature sensor makes the car run poorly. So I guess the only thing left is the AFM somehow

 

Sometimes rev hanging can indicate a lean condition.

 

Hello! I am experiencing now the same problem, it idles at 1100rpm. Iti is strange because it used to run great until I changed the upper timing cover. I know sounds funny but I had to take the intake pipe out with the ISV pipe that is bolted to it and when bolted everything back together started doing like this. Tried all above and still the same. I have replaced the vacuum lines and it still does it. Took out the breather pipe and blocked it, still the same. I have to say that otherwise car is running sweet, apart from the idle.Any other suggestions?