I have a 91 Montero that we just had the ECU gone through and repaired and the repair facility is telling us to remove the idle speed motor of the idle speed control but we want to make sure that after that item is taken out is there any other part involved to make sure there is nothing else from that sending information to the computer. The guy told us that we could just manually adjust the idle and not reinstall a new ISC. Any thoughts, help, suggestions would be greatly appreciated.

I would get my car out of there pronto.

That sounds like p*ss poor advice to me - others may disagree, but the system was designed to utilize the stepper motor. My concern would be that disconnecting the stepper motor might cause the ECU to go into open loop mode and your fuel mileage would suffer. I'm not sure it would cause that, but in any event the problem could still be in the ECU and not in the stepper motor. With advance apologies for the length of the post, here's how to find out where the problem lies:

Check ISC Operation Sound

1) Listen while you turn on the ignition. You should be able to hear the stepper motor kick in as you turn the ignition switch to "ON" (without starting the engine).

2) If you don't hear the operation sound, check the stepper motor circuit (if the circuit is normal, the problem is probably the in the stepper motor operation or the ECU).

Check Coil Resistance

1) Disconnect the connector. Note 6 pins (2 rows of 3 pins) on the ISC - they are numbered 1-2-3 (top row, left to right), 4-5-6 (bottom row, left to right).

2) Measure resistance between terminal 2 and terminal 1 or terminal 3. At 70 degrees you should read 28-33 ohms.

3) Measure resistance between terminal 5 and terminal 6 or terminal 4. At 70 degrees you should read 28-33 ohms.

Check ISC Operation

1) Remove the throttle body.

2) Remove the stepper motor.

3) Connect the positive (+) terminal of a 6vdc lantern battery to terminals 2 AND 5 of the connector.

4) Hold the stepper motor in your hand so that a finger or thumb is on the tip. Connect the negative (-) terminal of the battery to each terminal in the sequence described below, and check whether or not there is tip vibration as a result of stepper motor activation.
a) negative to terminal 3 and terminal 6
b) negative to terminal 1 and terminal 6
c) negative to terminal 1 and terminal 4
d) negative to terminal 3 and terminal 4
e) negative to terminal 3 and terminal 6
Repeat the test in the reverse (e-a) sequence.

6) If you feel vibration in all combinations, the stepper motor is normal.

If the stepper motor passes the tests, I think I'd have another conversation with the fellow who repaired the ECU.

Good luck,
Frank

Did you get your ECU repaired by AVPRO?? I had the same problem with mine (ISC blowing some parts in the ECU) and sent it to them. I forget the name of the person I talked to, but he also recommended that I simply unplug the ISC. After looking at the price for a new one, I went ahead and tried it. I had to adjust the pintle of the ISC a few times until the truck idled at 800ish RPM. That was approximately 6K miles ago. The ECU adjusts the idle up or down as necessary. Turning on the AC with the truck idling in gear does drop RPM slightly, but it is not a problem at all. I am getting around 15 MPG, which may be a little low??? I have had no ill effects from this at all (hot weather or very cold here). So if you want to, give it a shot. My truck is a 1990, but I do not think there are huge differences in the ISC/ECU among years. Good Luck <img src="/forums/images/graemlins/wink.gif" alt="" />

I did get it done by avpro just unsure if just removing the isc is all I have to do, is there another part involved like a sensor?

Here is what you need to do:

1) Unplug the electrical connector to the ISC
2) Start the truck and check the idle speed.
3) If the idle is too high or too low (should be 700-800), remove the ISC (3 screws) then turn the pintle of the ISC either in or out to adjust the idle.
4) Reinstall the ISC, leaving the electrical connection unplugged.
5) Repeat this process until you get the idle in the acceptable range.

You also may want to clean the ISC and throttle body. This will help with idling. I know this is a hokey fix, but it has worked just fine for me.

ISC/IAC Data and Repair Links

Here is a good page about the ISC along with some links of places that will repair it for you. They only charge $90. If that is in your budget I think it is worth having it function properly.

As far as removing the IAC; I do not think they meant to remove it, you should just unplug it and then adjust it manually as noted in a previous post.

Yes, possibly. There is a Throttle Position Sensor and an Idle Position Switch plus a Fixed SAS adjustment procedure.

However, if you intend to disconnect the ISC, there's no need to do any further diagnosis. If you want to find the problem and try to fix it, begin with a check of the ISC.

Good luck,
Frank

I have tested the ISC and any thing that has to do with terminal 3 wont work. I also tried to disconnect the ISC as advised and still have the original problem. It will start, run for about 10-15 seconds and then die. It will start immediatly and just keep doing this. It still has the same 42 fault code as before the computer was fixed. 91 Monty 3.0. Any help would be great. <img src="/forums/images/graemlins/angry.gif" alt="" />

Sounds like the ISC unit is bad. See if you can get one cheap at a junk yard and test it before you buy.

Let's cover a few other things and see if you can get it to run, though:

Will it run if you keep the rpms above idle after it starts? If not, when did you last change the fuel filter?

When did you last change the PCV valve? To test: Disconnect the PCV valve hose on the front of the intake manifold and apply vacuum - it should leak with vacuum applied. If not, replace the valve - it's tough to get to - buried under the upper intake plenum on the rear of the driver side valve cover.

When did you last replace the EGR valve? To test: remove the EGR valve, check for carbon deposits and clean if necessary. Apply vacuum of ~19.6 in.Hg and check for air tightness. Blow in air from one passage of the EGR and check for air passage at 11 in.Hg or more - at 2.8 in.Hg or less, air should not pass.

Check all around the engine for cracked or loose vacuum lines - particularly the purge control valve hose. The hose is attached to the round canister next to the coolant overflow bottle - runs to the purge control solenoid valve.

To test the the purge control solenoid valve - remove the connector and measure resistance - standard value is 36-44 ohms at 70 degrees. Disconnect the hose from the intake to the valve and blow in it - it should be closed when the engine is off and open when the engine is above 1500 rpms. Apply 12vdc to the terminals - should not hold vacuum.

Throttle position sensor (next to the ISC) - should read 3.5k-6.5K ohms at closed throttle.... should read 0.4-1.0vdc output voltage.

That should get you started - post back if we can help. Others may have some additional suggestions or short cuts.

Good luck,
Frank