Hi mate when you got out of the car and went to the engine it sounded as if it was sucking in air a bit like a pop charger but its got a std air box, strange, there's got to be a fault code pop up, also have you managed to successfully do the pedal dance as above because this should reset it, I had to do it once similar thing I had the plenum off etc and then put the key in the ignition and turned the radio on, the instant I did it I knew I should not have, I did the pedal dance and it was fine.I tried using a stopwatch etc but in the end I just read through loads of times so I knew in my mind and then counted it in my head worked first time.