Hi Chris, the speed sensor, injectors, O2 sensor, and ignition coils are all supplied battery voltage from a relay (K46 engine control relay) in relay/fuse box n/s engine bay. Relay is earthed (triggered) by ecu. If this wire from relay earth to ecu had an intermittent break, that could be your problem, or possibly relay itself. Also supplied is fuel pump, so fault would have to be intermittent/momentary or car would cut out, must be a judder or stall though. I am guessing that the car is 2000 - on. Tom