Generally, it is not the input signal that fails, it is the ISC motor that fails. You turn on the AC, the ECU tells the ISC to bump up the Idle speed and the idle speed does not bump up, because the ISC is broken.

Your idle speed drops when you turn on the AC because of the extra load on the engine.


'90 Montero XLS (Sold, sadly)
'95 Montero LS 160k
'03 Montero Limited 30k