Hi total novice so please be kind . My 06 plate 1.4 petrol has a weird fault. When I start up the engine revs and drops all the time and if I reverse it still revs and drops until I move forward and can rev higher than tick over. I've had it to a local garage and no fault codes showed up. Looking through other posts I think it might be something to do with the idle air control valve/ stepper motor( heard it called both). If anyone thinks it is this could you let me know where it is in the engine compartment and how easy is it to change preferably with nice easy pictures lol. Thanks