my c class 250 td has gone mad. on the wrong day it will not start. all the das lights come on and of when they want. when started there is sometimes power sometimes not. i can drive for ever or experience no gear changes with the auto box.its 1999 model and all is fine except this intermittent problem .the battery / engine earth etc are all fine. when the system isstable its all great. lease were DO I START TO LOOK TO FIND THE REASON.