Hi have recently had my 01 wrx in the garage 4 a diagnostic check and it shows no faults but the car is still missing and is most noticeable in 4th and fifth gear at about 50 mph, is ok with foot lightly on throttle but when i floor it in those gears it gets quite bad? Have changed plugs recently air filter and fuel filter to try and elimanate easy things..... any ideas?

Thanks in advance

 

Sounds like one of the coils packs is kaput.
Buy one new one and try it in each position until you get the right one.

 

From my experience change the one next to the turbo first as it gets the hottest