The stepper motor is a weak point on some of these engines. This is a very short guide to how it works
The stepper motor
You will need some torx keys and a screw driver for the plug.
First, take off the tb (disconnect the cable and hoses, undo the 4 bolts holding it in and the cable for the stepper motor). The tb is usually filthy, so giving it a good clean with thinners is a start
The motor is held on with 3 T25 bolts. Once off, inspect it for cracks, condensation, rattling etc.
This is what one looks like taken apart
A very simple setup, it has a motor on a worm, attached to a gear which moves the butterfly on the tb. The casing is waterproofed with a rubber surround and the contacts slot nice as pie into each other. If you have the unit like this, the casing tabs are most likely broken. The sensor is a sealed unit within the casing and cannot be tampered with (except with a hammer). The sensor wheel is after the gear, it is independent of the gear and can move of its own accord. This means if the motor is sticking (resulting in weird idling), the correct amount of spacers can be used so the tb only interacts with the sensor wheel and not the gear. Approx 3 spacers can achieve this (first photo)
Conclusion
I hope this guide was some help, if I've missed something or need further advice please leave a comment!
