Engine management warning light came on as I was driving very slowly. My Scooby is a WRX Pro-drive 2005, totally standard and trouble-free. It has a hunting, snatchy tick-over and is snatchy at low throttle openings, i.e. in traffic.
Took it the Subaru main dealer to fix the problem and service it (£340) but the didn't fix the problem and said it was indicating lean running, possibly an intermittent fault with the air flow meter. Engine light came back on before I got home.

I flipped the bonnet, popped the air box cover and found that the air filter was extremely distorted, the filter's metal sides were bowed, letting air past and the element was a real mess, all lifted up, as though the intake suction had ripped it apart. Rather like the element had gradually blocked and could not deliver the air the engine needs when I welly it.

I connected my fault meter to the car and got PO171, lean running indicated.

I have ordered a K&N performance replacement that replaces the dirty old paper one.

Could this have been the cause of my lumpy and lean running?

Nick

 

had the same fault recently mate it happened to be a split in the induction hose to the turbo. check all hoses for splits or any that have come loose.

 

I got a K&N performance air filter and it was the answer. The car doesn't ****** at low rpm, ticks over like an old diesel canal boat, breathes easily again and the revs rise quickly into licence losing territory. My local Subaru specialists also spotted the exhaust leaked from the middle section (mild steel) and from a fracture round the rear box junction (SS). Got a new straight-thu (SS) mid section, and it burbles sweetly and goes like a dream.
My main dealer will never see me again!
Nick