[DMGRS]

Originally Posted by Yorkshire GOC

This sounds the same problem you have - the IMG is mentioned but also an air/ vacuum leak .


https://www.mg-rover.org/threads/ver...histle.349599/

I found this thread a while ago when trying to help a friend with an MGF resolve a similar issue - his was indeed a very old (possibly original) IMG however on the K Series it's quite a different design (I am assuming you have a V6).

It could also be the exhaust manifold gasket - higher gas pressures at high RPM could be allowing a small leak to slip by.
Check for any carbon deposits around the exhaust manifolds, it should be easy to see if this is the cause of the problem. If it is we have them here: https://www.dmgrs.co.uk/products/kv6...-all-v6-models