V12 MERCEDES THROTTLE BODY ACTUATOR REPAIR
COMMON CAUSE OF THROTTLE BODY FAILURE
Most Mercedes throttle body failures occur with model years ’91-’96. The cause is commonly deterioration of the wiring harness. Over time the insulation becomes defective and allows the conductors to touch one another. This results in a poor running engine (if at all), high/low idle, poor acceleration and many other weird symptoms. Mercedes/VDO/Bosch removed the external harness on future models when it was identified as being the problem.
If you suspect that your throttle body is defective, take a small pen-knife and make a one inch slit in the outer sheath of the harness. Bend the harness so that you can look inside. If defective you will see copper wires touching one another. If you find that the wires/insulation inside are intact, there’s a good chance the throttle body is not the problem.
It’s also worth the time to take a look at the engine wiring harness. Look particularly at the harness near the temp sensor on the water neck, harness wiring going to the mass air meter, wiring near the injectors, and the wiring harness going to the coils. (make a small slit in outer cover)
On the V12's take a look at the harness at the rear of the alternator and the wiring going to the oil pressure sender.