When I try to start my car the glow plug light does not come on anymore and starts real rough, Im guessing I have some bad glow plugs? Funny thing is, the glow plug light does not come on right away but does come on when the car is started and stays on for about one minute. I know there is a after glow on this car when the temp is cold, why would the plugs work after the car is started and not before the car is started?