I know some on here have disconnected their IACs, and set the base idle using the screw on top of the throttle body. You might try this as a diagnostic to see if the lack of idle at normal operating temperature goes away. If it does, certainly your IAC is most likely the culprit.

I recently replaced mine with a new IAC from dsmisc.com... I don't know how price/shipping to UK compares to your EBay find though.

Best of luck to you!

Eric W.

'89 Dodge Raider -- 3.0L V6, MT, SWB