Missfire/stuttering

[Jordan_gti]

Just bought a 2002 (52) plate Golf Gti 1.8t (aum) engine. It has what seems like a Missfire, but I have changed the spark plugs,  and ignition coils, and it hadn't worked, it feels like the turbo boosts and stops then boosts again

[lemski]

N75 valve. Vac leak.
Ive had them where they feel like a misfire but its because the n75 is messing up

[Jordan_gti]

Ive just scanned it with my dads memoscan, its throwing up P0321 , P0172 & a throttle position sensor, do any of these go along with the n75?

[lemski]

1St code is engine speed signal from a quick look on rosswiki -which is crank sensor... Which could be the problem when its trying to get up in the revs
Seconds is the lambda after the cat.

[Jordan_gti]

where is the crank sensor located? gunna try to clean it up

[lemski]

Front of the engine in the block to the left of the oil filter if i remeber correctly. Held in by 1 16sided bolt which is 10mm. Theyre abit arkward to get out some times