A4 2.5tdi

[jmn]

My 1998 A4 2.5 V6 TDI is coming up for MOT shortly. The car has done 94k miles and has always been properly serviced.
It always seems to be a struggle to get it through emissions tests at MOT time. The car runs perfectly and I have travelled nearly 40k miles in 2 years. Just about all of my mileage is motorway.
The only fault code showing is 'low inlet manifold pressure'.
Fuel/air filters are changed every year. Oil is changed every 7.5k miles.
I have added injector cleaner twice over 40k miles.
No excessive smoke from exhaust.
No loss of performance.
No excessive fuel consumption (averages about 45mpg).
Can anyone suggest what may be causing this problem?

[sleep envy]

how hard do you drive the car?

[AdrianR]

Possibly needs a good thrashing to blow the soot out of the exhaust.

MOT man will rev it to 5K from idle several times - if you haven't blown the muck out of it, then this will and you will get a 'bad' reading.

AdrianR

[jmn]

Probably not hard enough by the sound of it-mind you it is difficult with an indicated 80mph being just over 2250 rpm in sixth...

[sleep envy]

try 3rd at 80 mph