I've got a MY98 JDM Forester. Recently my fuel pump died, and I replaced it with the Walbro 255HP, which I subsequently learned is not the ideal replacement as it would result in overfuelling, it seemed to be giving worse fuel economy than usual, so I figured I would install a 190lph unit soon. The engine seemed fine for a few weeks, did not notice any problems.
While out running around tonight, I felt some hesitation on acceleration, I did a few acceleration bursts to try and assess what is happening, but cant seem to come up with a fixed pattern, if i go WOT from say 2500 to 5000, engine would feel hesitant at first and seem to 'catch up' and surge a bit, if i come off throttle and repeat quickly, it seems fine on the repeat, on some bursts, I felt a 'pop' that i could feel on my foot through the throttle .
I parked up at home and lifted the bonnet, car idling perfectly at 700rpm, I pulled off the MAF connector, and it stayed the same! No hesitation, no stalling, ive done this in the past and it caused a stall, so It seems to be a bad MAF while I was busy wondering that the problem was from overfuelling (?). Again, the engine idles perfeclty, and generally drives fine, only very lately this WOT acceleration produces any problem at all.
I did a ECU reset using the under dash connectors, and it flashed the all-clear, no error codes.
Is this a guaranteed MAF failure?
My problem now is that its a grey import in the caribbean, and I think i will win the lottery before I find a good MY98 MAF sensor, can I use a MAF from other years as replacement? This one has the 3 pin connector.

 

Well to add to this I took out the MAF today and gave it a cleaning with non residue contact cleaner, and put some on the connector too, I reassembled it and started the engine, and it DID stall on disconnecting the MAF, which is the normal routine, it ran fine without the MAF when the engine was hot ?!
Could all my problems described be purely from overfuelling?