Basic issue: When the engine is cold the car will start fine, but will then immediately cuts out. It restarts on the button. Occasionally when sitting at traffic lights/junctions it will cut out for no reason. Occasionally it will 'hunt' at idle and feel as though it is going to stall before settling down again. These issues are intermittent.
Full story: My sister had to call out the RAC this morning as she was having some trouble with her 2009 1.6 Petrol Focus.
When she started the car it cut out almost instantly, but re-started just fine. Not thinking much of it she drove on and when she got to the first set of traffic lights and dipped the clutch it cut out again. She says the engine management light came on, but I'm guessing it would if the engine stopped whilst the ignition was on anyway. The idle also seemed to raise and lower quite a bit as though it was going to stall. All these symptoms seemed to go away once the engine was warm. The next obvious step was to contact the RAC.
So the RAC came to her place of work, plugged in a diagnostics machine and found a historic 'key' fault logged in the ECU from some time ago, but not recent apparently. He offered to follow her home to get her spare key 'just in case' the key was causing the car to cut out although he hadn't seen it in all 50 years he'd been a mechanic, she declined as she didn't believe a key would cause an idle problem and decided to ring me instead.
Unfortunately by the time she'd rang me the RAC guy had left. I believe he left too soon - I'm not even sure he looked under the bonnet for anything obvious and to be honest and should have done a more thorough inspection of the vehicle to assess the 'real' problem not what he saw on the diagnostics machine.
So I thought I'd come here to ask for advice as I'm not actually able to see the vehicle, she's a bit worried about driving the car although I've told her to continue and ring the RAC if it happens again. My first thoughts were the Idle Control Valve (if fitted on this Focus, I know they were on the old model)? If not then would it be one of the other sensors playing up and just not reporting an error to the ECU?
Is there anything I can do myself to check it over for her - if an ICV is fitted where is it located because I will strip it down and clean it out? I'm very familiar with diesel commercial vehicles such as the Transit and Land Rover's but not so familiar with petrols as I don't work on them at all.
Any help or advice appreciated?