I had a limp mode issue with 2014 Q5 2.0TDi. Glow plug light coming on regularly and Stop / Start failing to operate, though I normally switch it out anyway. Turned out to be a leaking brake servo. Engine getting more air than expected. Fault first highlighted mass air flow sensor but swapping out didn't cure the fault. Servo was corroded and passing air. Also original battery in car measuring 12.36 volts 1 day after a 300 mile run may have added to S/S issue. New servo and replacement battery. Thanks to Vasstech Teesside for curing.
