black smoke at high revs?

[Bev_B]

Not sure how long my Audi A4 has been like this as I don't thrash it much, it blows black smoke out the exhaust at over 4K revs but doesn't lose power. It is due an oil change and has high miles, I've had the EGR valve, air filter and housing blown through and checked for error codes but nothing . I've got 1 week left on the MOT so need to get it sorted ASAP but obviously don't want to be spending £100's getting it sorted because being a 1998 model its just not worth it.
Would be grateful for any ideas on what the problem could be.

 

[StompOn]

most diesels will smoke under heavy throttle if there only pottered around in so give it a good run b4 ur mot ud be surprised havin worked in a garage theres been many times that weve had to rev the car a load of times b4 the emmsions test so it would pass. i was quiet shocked at just how smoky some of the ones that passed were...so i dont think its anything to worry about if you get blue smoke its bad cus then means turbo or piston rings or valve seals have gone.. im sure someone will correct me on this if im wrong and sorry if i am just going from my own experience from havin done some diesel mot's

 

[etronic]

Check you intage connections and hoses. Only small hole or loose clamp will result in smoke....