Right, I have an Audi A3 TDi 2005 8p Quattro with poor performance and poor MPG (44mpg on a run). Ever since I got the car last year it has never felt as powerful as my friends 2006 Audi A3 TDi 8p 2wd.
Last week I cleaned the EGR and Flapper Valve out and found for a few days the cars performace and MPG was spot on until the EGR Valve decided to start leaking casuing the MIL Light to come on. I replaced the EGR valve with genuine new one, cleaned the inlet manifold and reset the light using a Snapon error code and diagnostic reader. The performance and MPG has gone back to how it was originally which is rubbish. I have had all the boost and vacume hoses off and can't see any issues with them. I have also swapped over the vacuum control module on the bulkhead and the MAF sensor from my friends car but this didn't make any difference.
My next port of call is to swap over the boost sensor on the bottom pipe and the flapper valve itself to see if this makes difference aswell as checking the Cam Belt Timing to make sure this is spot on.
Any other suggestions as to what I can check as this is starting to drive me mad and may have to book it in with someone who has the gear to test everything.
Any help on this would be appreciated.