Unless I'm losing it
, your Auxiliary Air Bypass Valve is operating the wrong way round.
When the engine is cold it needs extra fuel in the air/fuel mix. To do this the valve is open when the engine is cold. This means that when the throttle butterfly is closed (as in the idle position) there is an increased flow of air bypassing the throttle butterfly and therefore causing the Air Flow Meter to record more air intake (and hence more fuel required) for any given throttle position.
When the engine is warmed up, the Bypass Valve should be fully (or almost fully shut) so that all air into the engine is regulated by the throttle position and the setting of the idle screw.
One of the manual tests for the valve is to run the engine up to operating temp and then clamp the rubber pipes on one side of the valve. Clamping a pipe should not cause the revs to dip by more than ~50rpm. In other words, the valve should be as good as closed at full engine temp.
Or else I was very very drunk when I worked that all out!?
P.S. I can give you a spare when you are over!
