running fault/flat spot
 

afternoon all having some problems with my 19997 version 4 sti type r.
Fault: when driving and hitting around 3500rpm ie boost the car flat spots and there is no response let of the accelerator pedal and allow the revs to drop and it may pass or will keep doing this I have replaced the fuel pump as I thought this was giving the problem. the car has no pattern to when this happens it can be fine all day then just happen.

Car its self is standard apart from blitz exhaust and a new 255 fuel pump should I be looking at either boost solenoid or maybe air flow meter ?

have no eml coming and no flash codes come up when checked so just looking for a possible cause

Peter