Air Flow Meter
 

I have 56 reg Impreza 2.0 r sport 25,000 miles and it started stuttering 200 miles after i bought it , have changed teh plugs and local chap changed the air flow meter for a patterned part , stuttering stopped for most part but revs up and down at idle and as soon as i dip the clutch pulling up to lights or junction revs drop to zero and invariably now stalls . Is the patterned part no good and does it need a £300 subaru air flow meter (sensor) or is there another issue ? Has just had new oil/air and oil filters