Ryan,

I do not know the M104, just the CSI-E fuel system which I believe you also have. If so, the "flapper" can be seen when you remove the air filter box. It's brass and round maybe four inches in diameter. When you open the throttle, the butterfly at the start of the intake (below the flapper) opens. The extra air the motor now pulls will suck that flapper down. That flapper has a lever that pivots near the O2/idle screw and pushes UP on the plunger in the middle of the FD = fuel distributor (the round silver "thing" with all the fuel lines attached to it) to deliver more fuel.

You need to remove all of the fuel lines and the three Torx bolts in the middle to pull the FD. Once there, you will see the plunger. If you loosen the outer nut you will be able to rotate the inner section around the plunger which will move the plunger with it. Turn it into the FD body for less fuel and turn it out for more fuel.

HTH!

EDIT: I call the main brain the ECU. In my M103 / W124 3.0 it sits behind the battery on the passenger side between the MAS control unit which is really just a relay box (solid state I presume) and the OVP relay. The ECU on my US car has three rows on the connector. The non-US cars seem to have wiring harnesses with two row ECU connectors.

There is another "brain box" behind the ECU, which I presume is the ABS control unit. Anyone know for sure?