350i Flapper Injection Idle problem?

[sadbloke]

Just had a new engine fitted less than 100 miles ago, the throttle response for rising revs is instant, however, engine revs return to set idle speed appears to take too long? to stablilize. If the engine is run at say 3000 rpm then the throttle closed it does start to drop straight away but takes at least 10 seconds to return to the set idle. It is similar if hot or cold. Is this normal ???????????????????

[greenv8s]

Is there an overun flap valve on the plenum?

[wedg1e]

Sticking/ kinked throttle cable? Throttle return spring in place?

[sadbloke]

The butterfly, linkage and cable are fine, all closed fully. The over-run valve is operating as expected, checked with vacuum gauge and confirmed by blanking off the pipe just in case.

[greenv8s]

No it isn't normal. There's air getting into the plenum from somewhere and you need to find out where. You could start by blocking all the vac/breather inlets and see if that makes any difference.

[FrenchTVR]

A little squirt of WD40 in any suspect areas should help to prove it, it will make the revs rise.