Nuttynotty

Ok update.
I found that the turbo bypass valve is faulty and is broken closed so no air can bypass the turbo on idle, I believe that this will cause the turbo to try and run backwards because of the pressure when the throttle valve is closed. Well this is how I understand the bypass valve, i beleve that the bypass valve is used to reduce the pressure so its equale on both sides.could this blocked / closed bypass valve be causing al my problems ......?

I,m off to see if napa has one ...... Yer right.


Your thoughts please

yodasfro

Could be part of your problem I'd look on ebay for a metal BPV
(search term Bosch Turbo Bypass Valve for Audi Porsche VW Volvo Diverter) or a bosch 710n about the same price. The metal unit will last much longer as it has no diaphragm to fail. Stock bpv comparison
http://www.s4biturbo.com/art-dvtests2.php

How it works http://www.sjmautotechnik.com/troubl.../20vbypas.html

Nuttynotty

Hi Yodasfro,

I took the Bypass valve off late last night just to get to a loose bolt I saw....
The Bypass valve which was installed by the PO was not a stock Bosch part but it looks like a Chinese knock off, Aluminum and Brass….. Brass being the slider inside, well we all know what happens to two different type of metal when under heat. The Bypass valve has stuck closed when warm, could not move it even with a screwdriver handle pushing up into the removed valve assy.. there was no way the intake manifold pressure would move that sucker….
It is all starting to make sense now, if the valve could not release the pressure when on Idle the air has to go somewhere ??? the Idle valve could not cope with this extra air, hence the 2121 engine code ( could not correct the idle).

On to E bay or 034 have a nice one for $95.00

Updates to follow… Finger crossed 

Prospeeder

What your saying isnt really how turbos work. It cant spin backwards. Exhaust is driving it which is always going one direction. It doesnt spin fast enough to make any pressure or suction or any "more" air than normal, if anything it is slighty restrictive in a sense. Secondly, the bypass valve, alls its main goal to do is be closed at idle, and under conditions where pressure in the intake and pressure in the boost piping suddenly change(Letting off the gas suddenly) It Will open, so all the boost doesnt slam into the throttle plate and back out the turbo compressor. This action causes the compressor wheel to stop or slow alot and cause more wear

Prospeeder

or maybe i misread your post?? Doesnt your car idle high all the time, no matter what. not sure that would make the bypass valve a suspect.

Prospeeder

Yea i think i misread your posts , this part being bad is just gonna cause more wear, not really high idle condition. But it should definatly be replaced, hope it works.

Nuttynotty

Hi Guy’s

The Saga continues….. After installing a new Bypass valve and verifying that it is working, the idle condition is now worse… She now idles at 1200 RPM, and I now find that if I rev the engine very slowly increasing the RPM she gets to about 1600 RPM and the RPM will drop to 1000 and back up to 1600 and again drops back to 1000RPM this will continue till you release the throttle cable bring her back to 1200 RPM ( Idle), When she is doing this up and down revving I have disconnected the ISV with no change and also the TPS again with no change, its as if the computer is shutting down the fuel pump ?? turbo pressure is a .5 bars, and Fuel pressure is at 60 PSI.

The more things I find wrong / broken or leaking and fix the worse the car runs…….. This is so frustrating.
And the only Engine code is 2121 which is TPS or throttle cable adjustment both have been checked and double checked ( TPS is new), The TPS switch is working as when running the diagnostics moving the throttle activates the test sequence??


What else can affect the Idle, Im sure if I find what is causing the high idle I will find the cause of all my heartaches

Nuttynotty

This project… was a daily drive is now on hold. First off the timing pin came off the flywheel over the weekend whilst trying to fault find the high idle and no power at low RPM. Every sensor was verified over the weekend both at the sensor and at the ECU, nothing showed up being a problem. When running, she would start at 800rpm, and then clime up to 1200rpm when she started to warm up. The warmer she got the less power she had. Well that’s all by the way side now, no timing pin no start. No money.

How does a timing pin fall off?????

yodasfro

They usually get taken out by a foreign object most likely a ball bearing from the throw out bearing.

audi_marv

That's a bummer. I was going to suggest that you check out your idle control relay unit located in the aux. relay panel, that is if the 91'
model has this.