Update on Mini R56. The compression readings are very irregular.160 psi across all 4 cyls when engine is cold. When engine is warm and starts to missfire on cyl 1 the compression can drop to 75 psi and go back up to 135.Readings aren't constant when the engine is at running temp.Also when I disconnect the valvetronic servomotor at the back of cyl head it can idle normally,reconnect the motor and it still runs fine,then switch it off and restart and missfire is back immediately.I hope I'm making sense here.

Regards Dominic Casey.