Idle stuck at 3000 rpm

[borax]

I have a j plate 8v gti pb engine. I initially had issues with the idle going from 800 to about 3000 all on its own. I have done loads of things to try and solve it.......... Full service, plugs rotor arm, air filter, leads dist cap, mk3 rocker gasket, new blue sensor, new throttle body and new blanking tubes, and new gasket, at some point is has had a new isv. Now when I connect it all up it sits around 3000rpm adjusting the idle screw makes no difference.
I have checked all the pipe work and as far as I can see there are no. Vacuum leaks.

I currently have the isv feed to the throttle body blanked off and it runs/idles ok ish but I want to get it running spot on, anyone any ideas?

[Sgt_Lemon]

Does the fuel pump prime then switch off?

[borax]

I'm assuming fuel pump is ok, it runs ok with isv disconnected. How do I test fuel pump?.

Also, re problem, I have checked continuity between throttle switch, isv and ecu and it is fine

[Sgt_Lemon]

I was thinking to test the ecu.

[borax]

I will check. Im assuming you mean that if the pump doesn't stop priming there is an issue with the ECU. When checking this am i correct to assume that i need to listen to the fuel pump with the ignition on, then it goes quiet after a few seconds?

[Sgt_Lemon]

That's the one, if the pump doesn't turn off again the the ecu is shagged. If not then it's a nothing thing to tick off the list.

[borax]

OK so the pump primes OK and then turns off OK, vacuum leak i have missed??

[Sgt_Lemon]

To me it sounds to erratic to be vacuum, what have club gti said? Try looking at the wires to the dizzy, maybe hall sender.

[Mr Blue]

Have a look at the rubber intake pipe that joins to the maf sensor. Usually the speedo cable rubs through and causes un-regulated air to enter the inlet.