Help - Ford 2.9 V6 Engine Idles At 2000Rpm

Help,

My 1991 2.9 v6 has started to idle at +2000rpm most of the time. It doesn't seem to matter is it has just started from cold or is up to temperature but the issue seems to be intermittent (more often than not!).

I have tried the following: Cleaned the idle speed control valve (ICV), the throttle assembly, tried swapping out both the ICV and throttle position sensor/potentiometer (TPS) but with little joy - it just seemed to make it happen more often. The throttle cable is not sticking, Airflow Meters (AFM) idle mix screws are fully down to meet MoT emissions and the rocker cover breather hoses have been replaced. The plenum and fuel rail have both been off recently and although gaskets not replaced, they were smeared with liquid gasket before re-fitting.

I have also tried unplugging the coolant temperature sensor, TPS, ICV, AFMs (all one at a time) but all that achieved was to make it rev faster.

Sometimes it will drop to 1200-1500rpm when rolling but still not the 850-950rpm that it should be. When, on the rare occasions it does, as soon as I accelerate above 2000, that's it, fast idle resumes and will only fall below 2000 when clutch is out (driving) and the car is in gear crawling e.g. in traffic. If clutch is dipped, revs go to 1200ish which is correct as car is rolling.

WHAT ELSE CAN I TRY TO GET A NORMAL <1000rpm IDLE?

MRV