Power loss problem with 1997 A4 1.9 TDI

**john davis 100** · 30-04-2009,07:43 PM

Help please.I have a 1997 Audi A4 1.9 TDI and it keeps loosing power when pulling up hill or under load.I have had the car looked at and had a new air mass meter fitted,but that didn't help.It then showed an ECU fault so I had a replacement fitted (I bought from a breaker on line which was faulty and when I returned it under his 30 day warranty he denied ever receiving it and another £80 gone) this showed a G71 valve fault,which is exactly the same fault as the previous ECU had. I have just bought another replacement ECU (another £70) and had that fitted today,it was fine for 15 miles and then guess what?? The same fault again and when the Audi tecnician put the computer on it showed the same fault code and a faulty G71 valve. The car doesn't smoke or have any other faults and has covered 150000 miles,other than telling me to scrap the car,does anyone have any idea's???? I have spent quite a bit of money over the last 2 months and I am at my wits end and my overdraft limit. Thanks for any help

**kenney** · 30-04-2009,07:58 PM

What is your engine code?

**john davis 100** · 30-04-2009,08:45 PM

AFN I believe?

Thanks in advance for any help you can give

**kenney** · 30-04-2009,09:06 PM

Well to start with G is a symbol for a sensor or a sender and there is no such sensor as G71,you mentioned a valve,are you sure it is not N75 the charge pressure control solenoid valve,as this would cause the same symptoms you describe

**john davis 100** · 30-04-2009,10:20 PM

I think the fault code was G71 which indicates a mechanical valve within the ECU??

**kenney** · 01-05-2009,08:29 AM

Sorry john,i was a bit of track,there is the intake manifold pressure sender -G71- with intake manifold temperature sender -G72-which is a combined sensor,but this is not inside the ECU,

**john davis 100** · 01-05-2009,09:36 AM

Sorry,I know I am appearing a bit dull but the fault code was G71 on VAG-COM. I have been reading through the archives and someone had a problem very similar and lubricated the accuator to the VNT turbo??? Does this make any sense as they were having the same problem and fault code,but as that was the only one case I could find does this sound probable and is it a big job??

Thanks for your help in this matter as I am just about losing the plot with this,cheers

**ini** · 01-05-2009,01:18 PM

There is nothing wrong with your ECU, or the onboard MAP sensor.

If you are getting a 'manifold pressure sensor short to B+' or similar MAP error code associated with 'limp mode', it is most likely that you have a sticky turbo VNT mechanism.

**john davis 100** · 01-05-2009,05:53 PM

Is the sticky VNT difficult or expensive to resolve??

**ini** · 01-05-2009,06:03 PM

A dirty/sooted up VNT mechanism is a common cause of 'limp mode', and can be cured by either:

1. Heat - take the car for a very prolonged journey, preferably with the car loaded up with weight, or towing something if you have a towbar. The prolonged heat in the exhaust system will help to burn off some of the carbon buildup that is preventing the variable vane/ring mechanism from moving freely.

2. Dismantle the turbo and clean it out manually.

3. Chemically remove the carbon buildup from the turbo (Inotec turbo cleaner)

4. Swap in a fresh turbo (can be expensive and unnecessary)

There are many threads on sticky vnt and curing it. Search for 'limp mode' topics.

Most VAG dealerships will try and replace the complete turbo, as they do not class it as a repairable item.