Van came in to have both cambelts replaced and water pump and a new fuel filter. Done the job and road tested everything was good. Customer came back next day saying its a bit harder starting and when ignition switched off engine runs on for up to 2 mins. It has imobiliser unit fitted to rear of pump and when ignition is switched off theres no power down there. It seems to me that theres a fault with that but why did it start to play up now. Van just been purchased from e-bay. Customer keeps on that it was ok before belts fitted.

Any advice would be grateful