I have a problem when the car is stationary parked up sometimes it misfires and sometimes judders continuesly, not sure what the problem is? it has recently been serviced and i have had is diognostic tested however there is absolutly no fault anywhere, the car drives perfect locally and motorway without a problem, however i have this problem where is sometimes misfires and judders? the mechanic is unsue where the fault is, any ideas what it could be?