I own a 1996 Subaru Impreza AWD, 185K mileage, regularly serviced, never missed a beat until wife drove through deep water recently. Since developed an intermittent fault where engine coughs and power fades. Usually this is very brief, 2 or 3 seconds, then the car runs perfectly again. A couple of times the fault remained and power continues to fade making it necessary to pull over. Once, car relayed back.
Car in local non-Subaru garage who are generally good. They changed spark plugs, HT leads and installed new in-line fuel filter. No impovement though. No record on the engine management computor, so no guide there.
Strangely, a similar problem has just befallen my father in law who drove his Forester through deep water.