Re: Erratic idling/no power whilst car is warming up
Mine was diagnosed by an independent auto electrician; I can't remember whether it showed as an ECU fault code, or if it just showed as an out-of-spec value on the diagnostics. As for the cost, I don't know as it was done under warranty. It's always best in these circumstances to pay a few quid & have a diagnostic check done rather than just go ahead indiscriminately changing components in the hope that you hit on the right one - in many cases, when you fit the new part the system has to be recalibrated, so you'll need the diagnostic equipment for that.
Where are we going & why am I in this handcart?