The usual problem:
Jerky throttle, Limp Mode

A common fault showing up in BMW M3 M5 and M6 models is one or both throttle actuators failing, causing engine warning light and / or, limp mode, typically with error codes P1628 or P161F.

The cause

Inside the throttle actuator housing is a set of gears, and an electronic circuit which interfaces back to the ECU.
After 50,000 miles or so, the gears start to wear, resulting in sloppy meshing. This causes the electronics to work extra hard to try and respond to the erratically changing signals received, and if the gears are not replaced promptly, the power transistors in the electronic circuit become overloaded and burn out.

The solution

We can help with both the mechanical and the electronic faults.
BMW throttle actuator gears.
Through QDI, we offer a replacement gear kit for replacing the faulty gears.
More info on this below...
BMW throttle actuator electronics.
Through QER, we offer a repair service for the electronics, see below.

What to check for...

There are two throttle actuators, one for each throttle bank.
If one has started to go faulty, the chances are that the other will follow not too long afterwards, but if you want to just concentrate on the faulty one, and you have the read the fault codes, P1628 refers to bank 1, and P161F refers to bank 2.

Removing actuators from vehicle.

Please follow this link to our page for Removing throttle actuators page.

Fixing the bad gears.

Once you have removed the offending throttle actuator assembly from the vehicle, split the unit into the mechanical and electronic housings.
You can now inspect for excessive sloppiness in the gears, and it is quite likely you will find plastic swarf, as evidence of the slowly shredding gears.
Replace the faulty gears by using our kit, consisting of:
* A pair of replacement gears, which are precision manufactured from reinforced nylon (POM) and will last longer than the originals (which are just plain nylon).
* Detailed illustrated instructions, in English.
To replace the gears, you will need a bench vice, a socket set, a hammer and an angle grinder.
Detailed, illustrated instructions are provided with the kit, in English, and with these, the task is straightforward for any competent mechanic.

BMW throttle actuator gears repair kit instructions

The Illustrated instructions (above) show clearly how to strip down and reassemble the gear housing, including:

How to release the shaft holding the gear quadrant from the housing without causing any damage. How to safely remove the gear from the shaft. How to prepare the shaft for the new gear.
How to fix the new gear securely to the shaft.
How to safely re-assemble the gear and shaft to the housing.
How to tension the spring.

Save 20% and buy a 2 set kit

Checking the electronics.

Once you have removed the offending throttle actuator assembly from the vehicle, split the unit into the mechanical and electronic housings.
You can now inspect the electronic board for damage by examining the 4 arrowed FETS.
If any of these has turned a darker colour, its a sure sign that the FET has blown, although degradation of the FETs might have occurred, even if they look OK.
BMW throttle actuator electronics.
Even if all the FETS look OK, its a wise precaution to change them anyway as they could still be faulty, and even if they are not, they will have been stressed and are more likely to fail prematurely.

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Guarantee to our customers

All our products carry a full 1 year guarantee.
If a fault should develop at any time over the 12 month period, simply return for a free replacement or repair.

If, for any reason, you are unhappy with your purchase on receipt, simply return within 30 days for a full refund including P&P.