Hi guys sorry if im a pain

got a mk3 gti with an agg engine (8v). it will not rev past 4500 rpm, had a new dizzy and hall sensor, crank sensor, cleaned throttle body, new cam belt timed spot on!! fault code 00515 wont clear but think that's down to a faulty code reader, as it wont clear others stored.
Don't know if this helps, before I refitted the alternator drive belt I ran the car and it wouldn't rev past 3,000.
Any clue where I go next, airflow meter? lambda sensor?
Any help would be greatfully appretiated
1997
Car details, mk3 golf gti 8v 2.0
agg1633490 engine
Thanx in advance