Ferrari 412 Throttle Position Sensor Adjustment

Yes, it should "click" closed when the throttle linkage is in the idle position and then "click" open as soon as the throttle is opened. When at idle (and electrically closed), it "tells" the Microplex ignition ECU to retard the ignition timing by a few~5 degrees -- which makes setting the idle speed less fussy and less sensitive to the small unrepeatability of the throttle plates at idle. To check if is in proper adjustment and working, just unplug it at warm idle = the warm idle RPM should increase slightly when unplugged and then return to normal idle when plugged back in.

(The "click" is a good reference, but the switch contacts inside can still be bad even though it "clicks" properly.)

 

No, I don't have a schematic for the 412. The procedure for the idle adjustments would be to "short" the proper two pins in the wiring harness together (simulating a "closed' idle switch) so that the idle microswitch can be left physically "loose" and not impede the throttle plate mechanical adjustment(s). Then, afterwords, the idle microswitch final position is adjusted (to not affect the throttle plate position but to be closed at idle) and locked down. Unless the switch contacts are totally open, you should be able to determine which pins get connected at the "click" in the idle position with an Ohmmeter.

IME, the microswitch contacts are very good when the microswitch is new (near 0 Ohms), and still works OK if the switch contact resistance is just a few Ohms, but when the contact resistance gets up to 10~30 Ohms then the proper signal at idle does not reach the Microplex ECU and the warm idle will be higher than "normal".

 

Contact cleaner / Lighter fluid / Ultrasonic cleaner, can easily restore the switch to its former glory.

 

No need to open it: a generous amount of cleaner will find its way. You can also operate the switch under a reasonable load (~500mah?), the sparks will clean the contacts.