Idle Speed Controller (ISC) bad? (1 Viewer)

Jul 22, 2012
Seattle, WA
Hello all,

Not sure my ISC is working correctly - 1989 JF62 3FE with 278,XXX. Have followed the FI-71&72 steps in the Toyota Repair Manual. The resistance for all the terminals is within spec (19.9). I can feel the valve move when I ground each contact (S1,2,3,4) with battery voltage applied to B1 and B2. Even though I feel the valve move - it barely moves. I'm not clear from the Manual how much/little it is supposed to move. Video here: - at about 35 seconds in you can see it just move.

Symptom I am chasing down - during idle it would suddenly drop to 400/500 rpm'ish and then jump right back to a normal idle. Seems to happen randomly. Am working through the EFI section of the Manual as a learning experience/to see what's not working properly when I ran into this.

I'm hesitant to take the electrical part of the ISC apart to check it's guts - worth looking at?

Thanks in advance!
Oct 29, 2008
In the valley of the Great Salt Lake.
There are multiple systems on your engine that control the idle speed. Everything from the A/C idle up to the Power Steering idle up. I wouldn't necessarily zero in on the ISC any farther than you have already gone. If all the FSM checks are OK then it is most likely OK unless the actuator isn't moving far enough.

Did you check for engine codes? If not be sure and do that even if you don't have a check engine light on.

As I just also posted on another similar thread, I replaced the Fuel Pressure Regulator and Fuel Pulsation Dampener and fixed a similar problem on my rig. It is tempting to just throw parts at these things, but that can get expensive in a hurry. I think it is OK to replace parts like the pressure regulator and the pulsation dampener because they have rubber parts in them that are either already worn out or soon will be and they are known to cause the problems you are experiencing.
Jan 18, 2011
I had a problem with a similar- style ISC on a different vehicle. What helped a lot was to hook up
diagnostic lights to the leads on the ECU. You learn to read what the computer's asking
the ISC to do, and then you can tell whether it's the computer or something else that's causing problems.

I think the industry calls them 'noid lights or similar, and also uses them on fuel injectors.

In my case, it was an air flow meter, an air leak, and a bad wire in a harness...


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