My 1990 745 has a weird high idle on startup and a persistent high idle around 1000 rpms. I am testing the throttle position sensor (never had any failures before). To my simple brain, this looks like a dual switch: the middle terminal is ground, and the side terminals are either idle (in which case there is continuity with ground) or wide-open throttle (also giving continuity with ground.) When you move the throttle down to idle, the switch clicks and you get a continuous path from the idle terminal to the ground terminal. This tells the ECU that you want to be idling, and it activates the IAC.

In the case of this switch, it does not give this continuity. Anybody ever test one of these before? I am inclined to go buy a new one and see what happens.

Possibly could be fixed by disassembling and cleaning or flushing with contact cleaner, but definitely it isn't functioning correctly.

Now I'll go read the other posts and see what they say...

You can also test it with the OBD diagnostic socket. Ignition switch on, engine off. Plug the test lead in to socket 2. Place something in the throttle linkage to prevent the switch from closing. Press the button on the diagnostic link twice, the light should flash and you are in diagnostic mode 2. Now, rotate the throttle to WOT and hold it there. The light will stop flashing, and will begin to flash a response code. For WOT, the code is 333. Then the light will flash rapidly again. Now let the throttle return to idle. If ok, a response code of 332 will flash.

Bob,

Appearantly you possess some pretty detailed info on the use of the OBD - more than I've found in the 700/900 FAQ's or my Chilton's manual (emergency toilet paper). Can you share your source, or better yet, share the info itself?

Steve --

Next time you're under the hood, disconnect the two wires from the throttle switch and jump 'em together. See if it forces the IAC to take control.

Steve I have tested that same switch with a meter and your simple brain has it figured exactly right. It is a double throw micro switch and you must see continuity from the common terminal (gnd in this case) to one or the other of the other terminals.I know from experience with micro swiches on older style computer equipment that just because they click it does mean there is contact internally. I think replace it if you can't get it to test OK.