Just realized I never gave feedback/final resolution on this thread.
Turned out to be the sump breather hose (going down from the oil separator/CCV (Crank Case Vent Valve)) which had a tear in it . Created a vacuum leak.
Replaced the hose and then power,idle & startup was restored.
The original hose & connector was very brittle.
The rattle I heard was an exhaust manifold bracket near the bottom next to the sump. So that's sorted as well and wasn't VANOS (thank goodness).
Thank you everyone for your input! :ty:
Kind Regards