This is the first signs of a failed actuator. I've been looking into this project for a few months now and I've finally get there. Finding a spare S65 throttle actuator wasn't easy because of the BMW policy of keeping the old units replaced under warranty. I wanted to find what's happening and make something better. BMW dealers sometimes call it an electrical failure of the actuator but it's usually nothing to do with the electrics. They are very well sealed and look well made. The plastic moulded gears in the unit are made to a price, not longevity. Here are the parts laid out after dis assembly. The white compound gear in the middle of the picture is driven by the hard steel gear of the dc motor. Attached to the white gear is a 13 tooth reduction gear that drives the black output shaft with a lever on the other end of it's shaft which opens the bodies. The motor is driven against a hefty spring which keeps the throttle steady at any given throttle opening through the gear train. Here's the reduction gear. There is heavy wear on the teeth which is difficult to see in the photo. Any wear that happens on this reduction gear gets transferred to the plastic output gear. Again it's difficult to see but on close inspection you can see how thin the teeth are in the normal driving speed portion of the gear. The main white gear that runs on the steel motor gear shows no signs at all of any wear. This is mainly down to good engineering practice of using a plastic gear on a steel gear. This eliminates most of the wear and runs clean with no dust. However, the small reduction gear is part of the same moulding and runs on the plastic output shaft also made of plastic. Not a disaster, but plastic on plastic is a bit of a no no. This small gear not only takes a lot of torque through it when opening the throttles but also has to maintain speed by gently reciprocating backwards and forwards on the same teeth to do this. So, basically there's nothing wrong with the large white gear in itself. The problem stems from the attached reduction gear and the output gear which is moulded to the output shaft. I'm under warranty and have just started getting the dreaded idrive warning. If I take it to the dealers they will only replace the one actuator (still with the plastic moulded gears) . That means I will be back soon for the other one. Having spoken to various applications engineers, most of them favour making the gears out of Brass and Delrin 150 plastic. This is my brass and Delrin 150 reduction gear. Much stronger than the original and hopefully it will see me out. This is the oem output gear and shaft. The gear width is 10mm so by carefully offsetting the gears I've managed to get this width up to 11.3mm for some extra strength. This is my replacement gear viewed from both sides. Comparison between new and old with the shaft fitted. Finally assembled. Now I just need a spare morning to upgrade and fit both my actuators.