My son's 524 Turbo Deisel has a tach that stays on "0" until the car reaches 3000 RPM...then works normal until the car shifts...then the tach goes back to zero until the car shift again. The injector trouble light is on also. The car seems to run rough and then cleans up at the point the tach starts to work.....may be coincidence. I have checked the speed sensors and have looked over the wiring.... but to no avail. I have had it in the shop 3 times and they are not able to fix it either. Has anyone experience this one?