You probably need to start by pulling the front sensors and cleaning the sensor ends and toothed timing gear (which is part of the rotor). Should be able to clean the gear by spraying brake cleaner through the sensor hole. What happens is the fine metal dust gets attracted to the magnetic sensor whichs blocks the signal.

__________________
Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.