a4 2.0 tdi power loss

[cpr1974]

Help ! i have an A4 2.0 tdi B7 2005 160 thousand miles , it drives fine and pulls cleanly through the rev range with what seems good turbo boost but occasionally and happening more often it will loose power and will not rev past 3k and although i can hear the turbo spinning up its not anywhere near as prominent as normal , but feels like there is no turbo as it dont seem to spin up and kick in ! if you stop the car switch off the ignition for a few minuets then restart it will pull like a train again and drive lovely , no warnng lights come on pointing to anything wrong .
Any help would be much appreciated .....
thanks chris

[nevo]

You need a scan,see if its in limp mode.

[Crasher]

It is going into limp for either under or over boost. Underboost is usually a vacuum or wiring fault (the wires to the N75 valve tend to snap) but if it is overboost then in the vast majority of cases it needs the turbo rebuilding.

[cpr1974]

thanks crasher it would seem to happen when i boot it so would that indicate an over boost ? and ive plugged it up to a computer but not a vag com and it didnt show any thing and i would assume that you would get a light on in the dash to show limp home mode but there is nothing .......

[cpr1974]

but surly if it goes into limp mode it would have a light come on the dash ?

[Crasher]

No the MIL would not come on and your code reader missed the codes for the same reason, it is not an OBDII emissions errors.

[cpr1974]

so am i thinking only a vag com tool will find the issue , would a vag com hand held device find it or is it a trip to my local unhelpful audi dealer ?

[nevo]

Find someone in your area with vcds in the locations section,it'll only cost you some beers,then post the results.

[cpr1974]

brilliant thanks i will have a look and see what i come up with , thanks for the help

[Crasher]

It isn't just VCDS (née VAG-COM) that you can use but it is the most widely available, trustworthy and easy to use system.