Have a 2001 Subaru Legacy sedan that juts and bucks, seemed like transmission issue, Check Engine Light came on, got a reading of PO420 and a PO122 PO328 replaced the knock sensor, replace o2 sensors. it seemed all right for 4days and then it did the jut and buck again and then CEL PO328 but all ready replaced the knock sensor. At a loss on this. took it to a mechanic and he thinks maybe the brain box ECU? he said something about voltage not changing. he quoted like 500 bucks but if it is the ECU i see them on ebay from 50 to 200 bucks. any other thoughts would be helpful.