Idle System Troubleshooting '90 E30 325iC
 

My car idles a little high (1200) normally, but if I kick on the A/C it jumps up to 2500.

I've checked the hoses for leaks, and tested the ICV for the correct resistance values per the Pelican Parts article. I guess next is the Throttle Switch below the housing but I can barely get to it. I'm not getting any reading on my multimeter, and, assuming it either needs adjustment or replacement, what is the best way to reach/remove it?

Or maybe I should be looking at another system?

you may need to set the switch up properly. from memory the switch has 3 terminals and it has 2 sets of contacts, the switch closes one set at idle and one set at 60% to full throttle.
the setup requires you to back off the throttle stop screw so that the throttle lever just stops moving. then slacken the 2 Allen bolts just enough to allow movement of the switch.
with a multimeter set to continuity preferably with a buzzer connect 1 to the centre pin and one of the outside pins i cant remember which is which, but you should adjust the switch so that the idle contacts open just as the throtle starts to move, i seem to remember feeler blades between the stop screw and lever of about 0.45mm. But they do mount the switch in a silly place all the crud from the crank breather condenses in the switch and needs flushing with WD40.