Vehicle just about runs backfiring into inlet manifold, very little in the way of manifold vacuum (smoked it and no leaks), checked a couple of forums and the consensus is the Vanos control solonoid(s) are faulty. removed both control solenoids and supplied 12v feed both valves operate as far as I can tell. PWM signal to both solenoids is in low duty (no demand). My question is can these vanos units jam? Sounds like valve timing problem. Service history on this vehicle is non existent; and has had multiple oil changes and flushes to clean it up internally, although the solenoid valves seemed clean.

Thanks in advance

Mark