For the past month, intermittently, my mechanic (a good mechanic) has been trying to figure out what is causing my 2002 subaru forester to surge when when stopped, hesitate intermittently when stepping on gas pedal and generally run crappy. He's
1. replaced the fuel filter, run scans on the check engine light (says oxygen sensor is wearing out - he disconnected it as a test and still runs crappy)
2. checked out timing belt (is ok - put in new one 2 years ago)
3. replaced pcv
4. replaced temperature coolant sensor
5. (check engine code also came back for fuel trim problem - but Subaru doesn't have mass air flow sensor)
This car does have higher mileage than average - 150k
Help!! my mechanic is about to throw up his hands and I need my car back!