I am battling my 1999 Impreza Outback Sport's poor running issue right now. It had started running poorly at high rpms 4k+ a month or so ago then this week as I was driving home i had felt it sputter a few times at a steady cruising speed. Died at idle. Let sit for a day started and BARELY ran at idle but would run mid-throttle range and got me most of the way home. Same 0440 and 0420 codes have been showing for almost a year. Check fuel pressure before and after the under hood filter, nothing, doesn't even flicker. Fuel pump turned on and 10v + at the fuel pump according to my service manual. Replace pump, same thing. BARELY runs at idle and takes throttle ok until spark plugs foul out, BLACK and fuel soaked. 0 zero fuel pressure... pinch the line before the fuel rail when testing and still zero. Disconnect the line and when turning the key on it will fill a beaker about 250l when it primes for 2 seconds. I've found newer style pump housings crack but mine is the old style where the pump pumps straight up the fuel line.
