I am having erratic low idle problems (meaning it will surge up and down from almost dying to idling correctly) with my 87 Cherokee. Some of you may know I recently " aggresively" cleaned my Idle Valve.🤬 That said, when the Jeep is idling, either correctly at just a bit over 500 rpm, or too low, ( like just about to die); if I unplug the IAC valve, I get no change to the idle speed.
So, either the valve is bad, or, it is not receiving an electrical signal, right?

So is there a test for voltage at the connector that I can do before I lay out 50 bucks for a "good" valve?

As a side note, the jeep idled perfectly before I decided to "fix" the throttle body with a good cleaning. ( Sometimes you gotta just leave sh*t alone, Mike!)

 

The IAC is a "stepper motor". Testing the IAC itself requires a special tool. I don't know if there's a way to test it with some kind of device other than a VOM.

There is a caution in the FSM about "pulling" on the pintle too far as it might separate from the motor. It's possible you may have damaged it.

The FSM and the Renix Fuel Injection Manual show the wiring diagram and pinouts. I'd check the wiring first. Make sure the pins are in good shape and are making contact.

 

Is there a "known" voltage that should be at any of the pins in the connector? So that I can be certain that there is voltage to the valve.

 

This is the description of the IAC from the REM manual from Nick Risley, it is an explanation of the data you see on the REM for the IAC:

"This is an REM only reading that shows the estimated number of IAC rotations open or closed, with the count starting at 128. The IAC is a stepper motor, which requires the ECU to send individual pulses to rotate. Each pulse is indicated by an open or closed arrow, even if the counter has hit a limit.

Note: The ECU does not have position feedback of the IAC so it does not know if the valve is stuck, fully opened, or closed. The ECU will still continue to send pulses to try and correct the idle speed, which could cause the count to eventually hit a limit.

Note: The datastream will tell us if the IAC is currently being commanded open or closed, but not exactly how many pulses were sent so this number is only an estimate. The ECU can send multiple step pulses much faster then the datastream updates, and they will be missed by this count."

 

None that I could find. The diagrams from the FSM show this:

So it looks like you could check for continuity across the pair of pins on the IAC.



This is at the ecu. It doesn't show what might be power vs ground.

 

Thanks guys. But I am of limited brain space when it comes to understanding all of that. It may as well be written in Latin!

I will give it the cursory glance and check for obvious flaws in the electric wires and such. If I find none, I will gamble with 50 bucks worth of Idle Valve.

 

One last thing...what about the TPS? Could it affect the idle? I struggled to set it properly. If it is off, would that be an issue?

 

I think you get that the IAC has a cone that reduces or increases the amount of air that can enter the engine when the throttle valve is closed. I get it that the REM description is mostly gobbly gook, but in a nutshell it says the IAC motor is a servo. It is rotated a little bit at a time, in or out, by the ECM via electrical pulses. The ECM really has no idea where the IAC is in its travel, although it supposedly resets itself to baseline with the latch relay at start up. I don't think there is any way to test those ECM pulses without specialized equipment. And yes, the TPS definitely can affect idle. I'm swapping mine out with a NOS Mopar TPS this afternoon.

 

Like dmoe69 says. The TPS can affect idle. In my own experience a good TPS that's not adjusted properly results in a high idle. Mine idles very high when set to the spec %, so I have to adjust it down a bit.

Do you have the Renix Fuel Injection Manual? It's on Cruiser54's site. Page 66-68 cover the IAC.

I replaced my IAC a few years ago. I thought I saved it but can't seem to locate it right now. If I find it, I check the pins for resistance.

 

Great! Thanks for the help. Since it is ovef 100 degrees here in SW Missouri, it will have to wait for another day!

 

Note from DJ

For what it’s worth this information will only let you know that the two coils of wire are intact; no information as to how the Idle Step Motor is working!

Between A and D 50 Ohms and between C and B 50 Ohms.