The previous owner told me he balanced the throttle bodies, however, in the interest of learning ow to do this myself I purchased a Carbtune tool to help with this maintenance step.
The Carbtune allows you to view 4 of the TBs at the same time which I think is a big bonus in doing this maintenance vs. doing each TB individually.
They include some small orifice tubing to make restrictors otherwise the rods bounce up and down too much to get a reading. Since I already designed an inline restrictor for the gauges I sell I chose to use that instead
Plugs on the vacuum ports removed, lines plumbed in and connected to the Carbtune
This is how the first 4 throttle bodies are adjusted. From left to right it is cylinders 4,3,2,1
According to the BMW service manual the TB should be adjusted to 300mbar or 22.5cmHg so using a 7mm socket you tweak the adjusters to even out the readings. Turn left to reduce, turn right to increase.
Plugs on cylinders 5 & 6 removed and put onto 1 & 2, lines from the carbtune plumbed in
So using cylinders 3 & 4 for reference we adjust 5 & 6. From left to right 4,3,6,5
After adjustment. The car does idle better and when I checked the tach the needle used to sit at 1000rpm, now it sits a bit below it.