When investigating with my Foxwell NT510 scanner I found some “active” tests you could do which I assumed enabled you to turn various settings/solenoids on and off. I found some tests you could do on Vanos solenoids. When I activated and inactivated the inlet solenoid nothing much happened. When I “activated” the exhaust solenoid I thought there may have been a slight increase in revs but nothing more but when I “deactivated” it the engine immediately stalled. I repeated this procedure several times and it had the same effect?? I still suspect Vanos solenoids to be the culprit. I have ordered four replacements.