One of the few weak spots in the E90/E92/E93 M3 is the drive-by-wire throttle actuators. There are a number of reasons why they fail but we have found that the complete replacement is the only way to ensure the problem is fixed.
The M3 throttle valve actuators operate the individual throttle bodies on the S65 V8. There is one actuator for each bank. When the ECU sends throttle commands to the actuators they are supposed to open or close the throttles. At first the problem seemed to be weak plastic actuator gears that would slip and spin and not move the throttles. But we have also seen problems with the electronics control board. Therefore, complete replacement is the current best course of action.
Throttle actuator failure is almost always a sudden occurrence with no warning. If you scan and clear fault codes at every oil change you might catch a hidden "soft" code (2B21, 2B25) that might hint at an impending failure. Otherwise, consider replacing both actuators on a used car right away or every 3-4 years.
The actuator is the same for both engine banks and is the same for all E90, E92, and E93 M3 models.
This is the Genuine BMW actuator, branded as BMW, and the same unit you would buy from the BMW dealer (but at a substantial discount). It comes with a two year warranty.
E90 / E91 / E92 / E93 (06-13) > M3