You will have an issue with ELD (electronic load detector) P73's look for a voltage signal from the ELD via alternator and fusebox, when the ECU doesn't receive the signal the ECU automatically compensates by increasing the fuelling to raise the idle for services that load the engine. You will always have a higher idle(1050+~ rpm) I had this issue, did loads of research into it! PM me if you want any more info dude there are a few ways to sort it
Jimbo - whats can be done to combat this? had it when i bought the car with a Spoon ECU on it, changed to UKDM ECU, but might get a 98 Spec to match the exhaust i have on it now.