BMW M3: S65 V8 throttle actuator failure and limp mode

The S65 uses two electronically controlled throttle actuators, one per bank, to operate its individual throttle bodies. The internal gears and position sensors wear out with no reliable warning and no predictable mileage — cars simply develop the fault at some point — and when one fails the engine drops into limp mode with badly reduced power. Both actuators are usually replaced together because the second tends to follow the first. Alongside the rod bearings, this is the other item the enthusiast market expects to see addressed on a car of this age, and the parts are not cheap.

• Sudden loss of power / limp mode with an engine warning light
• Erratic or hunting idle
• Jerky or unpredictable throttle response
• Whirring or buzzing from the top of the engine

1. 1

   Ask directly whether the throttle actuators have been replaced and for the invoice — like the rod bearings, this is a known scheduled expense on these cars and a straight answer tells you how the car has been kept.

2. 2

   Start the engine and let it idle for a few minutes, listening for a whirring or buzzing from the top of the engine and watching the tachometer for an idle that hunts up and down rather than sitting steady.

3. 3

   On the test drive, use a range of throttle openings including small, gentle inputs, and feel for response that is jerky or does not match your foot.

4. 4

   Check the dash carefully for an engine warning light, including one that appears only after the car is fully warm.

5. 5

   Drive it long enough to get to full operating temperature, since the fault often shows up warm.

6. 6

   If a workshop inspection is possible: have the fault memory read for throttle actuator and adaptation codes, which log even when the light is not currently on.

$1,800 to $4,500 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

• “Have the throttle actuators been replaced, and do you have the invoice?”
• “Has the car ever gone into limp mode or lost power suddenly?”
• “Are there any stored fault codes?”

The failure described above is documented in published sources — owner forums, technical service bulletins, recall notices and workshop write-ups — held in our fault database. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them, and it is a starting point for an inspection rather than a manufacturer statement.