[paul r w]

Sorry for the delay in responding, I've only just got it fixed.
The cause of the problems were:

PVC Hose split at intake manifold, intake manifold needed to be removed to access the pipe and replace (note: pipe difficult to see behind the manifold).
Idle stepper motor was faulty as well due to being overworked through the excess air issue. When the pipe was replaced it wouldn't return to normal speed settings & was stuck at high speed.
Manifold seals also renewed at time of repair as these had signs of wear.

Regards Paul