trailturd Posted October 19, 2023 Share Posted October 19, 2023 87 Comanche 2.5, I'm having a idle issue and I'm having a hard time diagnosing the problem. The issue I'm having is that the idle stepper motor works intermittently. Originally, it wouldn't start without pressing on the gas pedal. Once warm it idled fine, but when cold the idle was low. Then I started to have issues with having to step on the pedal to start it and once started, sometimes it would be fine, other times it would rev to 2500-3000 instantly and not idle back down. I checked to see if the stepper motor was opening the butterfly at shut off and it was not. Figured the stepper motor was bad, replace it, and the TPS at the same time. Set the TPS with a multimeter per the instructions found here. https://cruiser54.com/?p=54 That didn't change anything, still had the random high idle and having to give it gas to start. After having it high idle every time I drove it for about a week. One day I went to drive it and the idle was back to normal, so I unplugged the stepper motor so that it couldn't change the idle, and that was fine, I just had to give it gas on start ups. Which was way better than it always trying to rev to the moon. Poking around under the hood to see if there was a sensor or something that would be messing up the information that the computer sees, I noticed that the temp sensor on the manifold just below the TPS had frayed and exposed wires. Hopeful that this was my problem, I replaced that sensor and still zero change. I'm at a loss. What signals the stepper motor to increase or decrease the rpm? I know it's from the computer, but what signals are the computer looking at? I just don't understand why it never opens the butterfly on shut off, but will randomly decide that the idle rpm needs to be 2500-3000rpm. For now I'm back to just driving with it unplugged and having to give it gas on start up. Other than that, everything else is normal. All ideas welcome, about to sell this thing if I can't figure this out. Link to comment Share on other sites More sharing options...
eaglescout526 Posted October 19, 2023 Share Posted October 19, 2023 The ISA is controlled by the ECU. Over time they will stick in various positions. In your case it got stuck low and then it got stuck high. The ISA is supposed to open the throttle after shut down so when you go to start, you won’t have to touch the gas pedal at all to start the Jeep. Sounds like to me the ISA needs a clean and rebuild. I do offer that as a service but it’s more of an exchange program where I get yours and I send a rebuilt working one. Link to comment Share on other sites More sharing options...
trailturd Posted October 20, 2023 Author Share Posted October 20, 2023 4 hours ago, eaglescout526 said: The ISA is controlled by the ECU. Over time they will stick in various positions. In your case it got stuck low and then it got stuck high. The ISA is supposed to open the throttle after shut down so when you go to start, you won’t have to touch the gas pedal at all to start the Jeep. Sounds like to me the ISA needs a clean and rebuild. I do offer that as a service but it’s more of an exchange program where I get yours and I send a rebuilt working one. Except that the isa is new, and I’m having the same problems Link to comment Share on other sites More sharing options...
eaglescout526 Posted October 20, 2023 Share Posted October 20, 2023 Ok. So did you do the adjustment procured for the ISA when you installed the new one? If the screw is too far out, the idle will go and remain high as the ECU tries to compensate and lower the ISA. If the screw is too low, then you’ll have the issue of starting along with idle being too low. Note to self, write this procedure in the DIY. Link to comment Share on other sites More sharing options...
trailturd Posted October 20, 2023 Author Share Posted October 20, 2023 7 minutes ago, eaglescout526 said: Ok. So did you do the adjustment procured for the ISA when you installed the new one? If the screw is too far out, the idle will go and remain high as the ECU tries to compensate and lower the ISA. If the screw is too low, then you’ll have the issue of starting along with idle being too low. Note to self, write this procedure in the DIY. Even new the isa never opened the butterfly after turning off the key. When the idle isn’t crazy high it will idle around 800 rpm so I believe I have it adjusted right. Link to comment Share on other sites More sharing options...
eaglescout526 Posted October 20, 2023 Share Posted October 20, 2023 Hmmmm peculiar. Link to comment Share on other sites More sharing options...
cruiser54 Posted October 20, 2023 Share Posted October 20, 2023 Whaddya wanna bet your poor idle is caused by a vacuum leak at the intake manifold? Bolts are notorious for backing out and there's a few hoses that crack also. Photo attached. Have you ever refreshed your firewall ground? Link to comment Share on other sites More sharing options...
White_Comanche Posted October 20, 2023 Share Posted October 20, 2023 19 hours ago, eaglescout526 said: Note to self, write this procedure in the DIY. I think this would be awesome, and would pretty much eliminate any confusion on the whole process. Well over a year ago we exchanged a few emails regarding you rebuilding my ISA. Never did follow through because I eventually found out that my motor was quite new around the same time I did extensive work in and around my throttle body. The few times my ISA got stuck it was during cold winter starts from it not being driven for a long while. I read pretty much all literature in various FSMs on the whole procedure. When parsing out the steps from their word usage, it really gets confusing. A Comanche Club post using modern language and photos to fall back on will be a great help! Link to comment Share on other sites More sharing options...
eaglescout526 Posted October 20, 2023 Share Posted October 20, 2023 I’ll work on the DIY this weekend. Link to comment Share on other sites More sharing options...
trailturd Posted October 20, 2023 Author Share Posted October 20, 2023 11 hours ago, cruiser54 said: Whaddya wanna bet your poor idle is caused by a vacuum leak at the intake manifold? Bolts are notorious for backing out and there's a few hoses that crack also. Photo attached. Have you ever refreshed your firewall ground? I’ll spray for leaks and double check/clean ground just to rule those out, but to be honest I don’t have high expectations. Link to comment Share on other sites More sharing options...
cruiser54 Posted October 21, 2023 Share Posted October 21, 2023 Welcome to working on cars............ Link to comment Share on other sites More sharing options...
White_Comanche Posted October 21, 2023 Share Posted October 21, 2023 Link to comment Share on other sites More sharing options...
trailturd Posted November 14, 2023 Author Share Posted November 14, 2023 So I sprayed carb cleaner all around the intake, throttle body, and vacuum lines while running and zero change in RPM. Cleaned and checked ground, no change. Now that it's gotten colder here, low 20's, high in the 50's it has not had the random high idle with the stepper motor plugged in. If anything the plunger has retracted and I was having to keep my foot on the gas to keep it from dying at stop lights. Once I had the motor warm, I adjusted the ISA to 800 rpm and it's been fine once the motor is warm. The ISA is still not opening on key off, or adjusting for cold idle. I still have to give it gas to start every time, and at stop lights until the engine is warm. What am I missing? Is there a intake air temp sensor on the manifold that could contribute to this if it's faulty? What other sensors should I be looking at that would effect the ISA moving? Link to comment Share on other sites More sharing options...
Ωhm Posted November 14, 2023 Share Posted November 14, 2023 1 hour ago, trailturd said: What other sensors should I be looking at that would effect the ISA moving? Not a sensor but the B+ Latch Relay is used for resetting the ISA for the next ENGINE START UP after the KEY is cycled OFF. Link to comment Share on other sites More sharing options...
trailturd Posted November 29, 2023 Author Share Posted November 29, 2023 On 11/14/2023 at 3:24 PM, Ωhm said: Not a sensor but the B+ Latch Relay is used for resetting the ISA for the next ENGINE START UP after the KEY is cycled OFF. Bought a new relay and tried it, as well as swapping the relay from the fuel pump, which I know is good. Started jeep and idle instantly went to 3000 and climbing before I could shut it off. Looked at the ISA and now it looks fully extended. Bottomed out the adjuster on the ISA and the idle is still high on start up, 1200-1500 and starts to climb as it warms up. ISA still does nothing after shutting off motor and taking key out. I'm at a loss here, not sure what else to check. Link to comment Share on other sites More sharing options...
trailturd Posted February 21 Author Share Posted February 21 So I wanted to give an update on this. Even though I had replaced the ISA recently, I narrowed it down to that with a continuity test on the stepper motor itself. Replaced it with a Crown brand this time and so far it's been working as intended. Link to comment Share on other sites More sharing options...
Ωhm Posted February 21 Share Posted February 21 Link to comment Share on other sites More sharing options...
brucecooner Posted February 22 Share Posted February 22 10 hours ago, trailturd said: So I wanted to give an update on this. Even though I had replaced the ISA recently, I narrowed it down to that with a continuity test on the stepper motor itself. Replaced it with a Crown brand this time and so far it's been working as intended. Is "ISA" the same as the "IAC" (Idle Air Control) ? I was getting those random 3000+ idle starts last summer, and replaced my IAC with one from Napa (set as per the included instructions). I would still get the high idle occasionally. Then the high idle issue disappeared last fall and I haven't seen it since, but I'm wondering if it's a warm weather behavior. If we're talking about the same thing, I'd love to have the test steps so if I see it again I can test my valve. I'll definitely get a Crown one if that's the issue. Link to comment Share on other sites More sharing options...
eaglescout526 Posted February 22 Share Posted February 22 1 hour ago, brucecooner said: ISA" the same as the "IAC" (Idle Air Control No. Similar in function but no. The IAC is not as serviceable as the ISA. IAC is 4.0L ONLY. ISA is 2.5L ONLY. From what I have heard about the IAC, is that it can get gummed up from carbon build up over time. Idle Speed Actuator Idle Air Controller Link to comment Share on other sites More sharing options...
brucecooner Posted February 22 Share Posted February 22 6 minutes ago, eaglescout526 said: No. Similar in function but no. The IAC is not as serviceable as the ISA. IAC is 4.0L ONLY. ISA is 2.5L ONLY. From what I have heard about the IAC, is that it can get gummed up from carbon build up over time. Idle Speed Actuator Idle Air Controller Ah, good to know. While cleaning the throttle body I did remove the old IAC to spray some fuel system cleaner in, and a lot of black buildup came out. But that didn't fix the high idle, hence its replacement. Link to comment Share on other sites More sharing options...
eaglescout526 Posted February 22 Share Posted February 22 11 minutes ago, brucecooner said: Ah, good to know. While cleaning the throttle body I did remove the old IAC to spray some fuel system cleaner in, and a lot of black buildup came out. But that didn't fix the high idle, hence its replacement. Sounds about right. I dont know much and have never owned a 4.0L to help out much. Ironically I have AMC books on the engine and it’s fuel system. Link to comment Share on other sites More sharing options...
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