Loss of Power

:aargh4: Hi everyone another newbie on the scene needing help. I have a 2002 VW Passat 1.9 Tdi 130bhp. Last week (when towing) I noticed that the car pulled as normal in 1st to 3rd gear. When I reached 4th it was ok but would suddenly loose power. The power loss would then be in all gears until the engine was switched off. This reset the engine and it was ok, but the problem would reoccur. It also does it solo when the engine is put under pressure. I've had it looked at and the fault was diagnosed as a faulty turbo charge pressure valve. This was replaced and made no difference. £80 down the drain! The car is not burning oil, blowing black smoke, overheating or using water. Also I am not getting any warnings displayed. Can anyone help, it's driving me mad. Thanks. Vinut21

Could be a faulty Mass Air Flow meter.

Thanks for that. Can you test to see if thats the problem before buying new. I changed the air filter just before this problem occured. Could I have upset something? Cheers