Possible to bench test an Idle Speed Control Valve?

Question

I just replaced the one on my car, a 1995 Escort, and I'm curious as to how this thing is supposed to work. the resistance across the coil is right, but when I apply voltages to it (anywhere from 8-25V DC) I really don't see anything resembling what I'd expect to see, but I do feel the coil being energized. If necessary I can send it a square wave or sine wave signal, etc., but I can't find anything on the internet explaining how it's supposed to work or exactly what I'm supposed to see. When energised I do some some movement in the parts, but not much. Obviously the part is bad because it fixed my idleing problem immediately when I replaced it, but I'd like to learn something if there is something to be learned before I throw it out.

Note: It had been cleaned maybe a year ago, and so I don't think it was that dirty. Possibly the reason I'm not seeing it do much is because it's broken.

clifto · Accepted Answer

It's pulse-width modulated.

Steve W. · Answer

It is nothing more than a solenoid with a monitor circuit in it. Throw a square wave through it at 12 volts and it should extend and retract on the pulses. It doesn't move much. Usually they no longer send the signal back to the ECM so it cannot control it properly.

Scott Dorsey · Answer

Bingo!  It's a solenoid that should open a little valve, but it isn't. Either because the valve is jammed or the solenoid has some shorted turns. --scott

scott21230 · Answer

It only has two wires going to it, so you are correct on the no feedback part. I can input a square wave to it. Yes, when I was applying straight voltage it only worked when i applied voltage in the correct polarity.

sdlomi2 · Answer

It is supposed to send a signal back to ECM so ECM can adjust voltage to it to properly control idle speed--it is when 'broken' that it no longer sends the signal back. It is probably grounded when in place(1 "wire"), a "2nd" wire controls it from ECM, and "3rd" wire is to send signal back to ECM. s

Steve W. · Answer

Yep. You have it correct. Just like most vehicle until the companies got  smart and started using ground wires to components to get cleaner signal  return.

Possible to bench test an Idle Speed Control Valve?

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