loosing boost on tdi 90 engine

[raepaul]

at times when i feel like puting the foot down a bit i tend to lose boost. i can go heavy footed for only a few miles and then feel a sudden "jolt" put the foot down again and boost is not there at all. i then stop, turn the car off and on imediately and its fine.

anyone have any ideas what this may be? the car is a seat ibiza tdi s 90bhp on a v plate

 

[Swig]

It could be going into "limp mode". Does the engine management light come on?

You should get someone to read the fault codes from your ECU using vagcom or similar.

I have a problem with similar symptoms - what happens on mine is the ECU detects that the turbo is producing too much boost and goes into limp mode (cuts fueling to stop the turbo spinning up). This protects the turbo but makes the car go slow, or rather accelerate slowly.

 

[sssstew]

yep, get vag com on it and see what it thinks is causing it to go into limp mode. Otherwise your just speculating.

 

[Muttley]

When this happened to me it was the EGR valve sticking open. Tended to happen at overtaking speeds on the motorway.

VAG-com will show positive pressure deviation - the EGR valve sticking open instead of closing allows too much pressure in from the exhaust as the engine revs rise, hence the positive pressure deviation i.e. overboost.

If you have the ALH engine, then it could also be sticking turbo vanes. All the other TDI 90 engines (AHU, AGR and the like) have wastegate turbochargers.