Audi A4 - 1998 1.9 TDI - 138,000 miles
Car has been running great prior to the following:
Coming to work this morning I had been driving about 10 miles, went onto a dual carriage way - tried to accelerate but had no power.
Car didn't stop but continued to have lack of power all the remaining 15 miles to work.
Stopped and started ok - ticks over ok.

Could it be the Air Mass Meter? I have had this changed within the last year so i am suspicious it cannot be this again!!! Last time when I changed the air mass meter the car lost power over a period of time not suddenly which has happended this time..

Any similiar experiences out there / advice / things to check.
If It is the AMM can I change it easily without special tools myself?

thanks in advance for any help..

Steve