I have a 400E, 119 motor, 140k, that has not been running right for quite a while. It idles rough, runs OK, but doesn't have as much power as it should. Basically everything is new on the car, wiring harness, spark plugs, wires, caps, rotors, coils, fuel pressure regulator, injectors (cleaned) and the problem persists. The problem has been traced by my mechanic, with diagnostic equipment, to one bank of cylinders, the passenger side. This would point to a distributor or problem or electrical problem on that side. But a new backing plate and rotor did nothing. He now thinks it's a cam timing problem of some sort. It just started up one day with the problem - ran fine the day before - there was no trauma of any kind. My question is this - what could cause cam timing to get out of whack like that? Or what else might the problem be? Thank you.