vectra TDI 1997 diesel?

i washed the engine with diesel and since then the car became very flat its drivable but very slow i could hardly over take any body , but on average speed i could go up to 70 or more but its gone relly bad in accelerating. i hope some body could help me with that as i took it to a garage and checked with computer and couldn't fix it.

adam
March 2010