why does engine idle revs more when cold ?

Sounds like the temp sensor in the throttle body failing and the mixture being sent through to the cylinders very rich in fuel. Once the sensor decides you're up to temp its reducing the fuel content in the mixture and therefore reducing the idle speed.

JBro
March 2015

Small PVC pipe from crankcase to inlet manifold leaking air

Mutley
March 2015

It could be any number of reasons you have this problem and a relevant computer would be the way to go to get live data during which it would be able to see what each sensor is doing at what particular time paying particular attention to coolant sensors and manifold/egr data,yes you could change this and that and get no further forward at great expense,also try google or a Ford forum and see what comes up there pertaining to your fault,good luck

cdc
March 2015