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Everything has been going good for a while and I knew it was too good to be true. The other day it intermittently would spike up to about a 2k idle speed when at stop lights but it was only here and there. Went out to warm it up before work yesterday and it raced a hair over 3k the entire time. After 10min of it not changing I shut it off and took the wife's car to work. I didn't start it up yet today but I anticipate the same result. I am thinking the idle stepper motor is screwing up. I don't know much about it though. Can I simply replace it with a parts store one and be driving it no problem or will I need to somehow calibrate it as well? I wouldn't sweat it so much if my scanner would connect to it when I plug it in to the OBD1 but it has no communication with my scanner and I don't know why. Feedback is appreciated!

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check for vacuum leaks.  :L:  including loose bolts holding the intake to the head.

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Clean idle air controller.

 

Also -- on the Renix models (which includes 1990), the accelerator cable doesn't connect the gas pedal directly to the throttle body. The cable goes to a bellcrank assembly that's mounted on the frame rail on the driver's side, below the brake master cylinder. The bellcrank is a pivot, and over the years the pivot can get dirty and rusty, restricting movement. Try spritzing it with PB Blaster.

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33 minutes ago, Jeep Driver said:

He has the 2.5 1990 would still be TBI and I doubt it his stepper motor.

 

I missed that.

 

Does the 2.5L use the bellcrank linkage?

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No. The accelerator pedal is lined directly to the throttle body. It can possibly seize up but the springs on the body could be an issue as well. The other thing is the stepper motor could have locked up into the ready to start position and that’s where it’s staying and not moving down like it should after initial start up. 

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It has been insanely cold and windy here so I really have done nothing more that a quick glance under the hood at obvious things. I drove it to work today because my wife needed the car and i refuse to drive the Gladiator in the Winter months. All I can say is I drove 10 total miles and didn't touch the gas pedal once, just clutch and shift and it was all go. The stepper motor looks like it is out further than it should be. Either way I want to replace it just due to age (appears original and the truck is over 210k). When I get a day that doesn't feel like Siberia outside I am replacing every vacuum line. They are all oil soaked and soft and it is a matter if time before failure, plus the PO has them spliced and hacked everywhere. My biggest concern is if I swap in a new stepper, is it simply plug and play or not. I have never dealt with one before. If the motor blows up before the part arrives I am at the point I could care less. It will give me a justifiable reason to to swap a carburated V8 in. In the meantime I am hoping I can bolt a new stepper on and go. Is it that easy or is there more to it?

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5 minutes ago, 90MJ said:

It has been insanely cold and windy here so I really have done nothing more that a quick glance under the hood at obvious things. I drove it to work today because my wife needed the car and i refuse to drive the Gladiator in the Winter months. All I can say is I drove 10 total miles and didn't touch the gas pedal once, just clutch and shift and it was all go. The stepper motor looks like it is out further than it should be. Either way I want to replace it just due to age (appears original and the truck is over 210k). When I get a day that doesn't feel like Siberia outside I am replacing every vacuum line. They are all oil soaked and soft and it is a matter if time before failure, plus the PO has them spliced and hacked everywhere. My biggest concern is if I swap in a new stepper, is it simply plug and play or not. I have never dealt with one before. If the motor blows up before the part arrives I am at the point I could care less. It will give me a justifiable reason to to swap a carburated V8 in. In the meantime I am hoping I can bolt a new stepper on and go. Is it that easy or is there more to it?

Unplug the stepper and forget about it. 

 

The plunger will thread in, adjust it to a fixed idle speed. 

 

 

The stepper is available, BWD, it's a total POS, don't bother. You will not find it listed for a Comanche, it will be listed for a 89 Cadillac Coupe de Ville, IIRC. 

 

 

My stepper actually works but it's new NOS on a NOS TBI, but I drove it for years with no stepper. 

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So ultimately I don't even need the stupid thing? You are saying it is basically going to become an idle screw that I set and that's it? Sounds too easy.

So what is the actual point of it? To increase idle at warm up or something?

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You can rebuild the stepper motor. Nickintimefilms on YouTube rebuilt his and it works fine

14 minutes ago, Jeep Driver said:

Unplug the stepper and forget about it. 

 

The plunger will thread in, adjust it to a fixed idle speed. 

 

 

The stepper is available, BWD, it's a total POS, don't bother. You will not find it listed for a Comanche, it will be listed for a 89 Cadillac Coupe de Ville, IIRC. 

 

 

My stepper actually works but it's new NOS on a NOS TBI, but I drove it for years with no stepper. 

Why doesn’t he need it? Renix uses it to adjust the speed of the engine at warm up and keeps a decent idle. 

Crown actually makes new units for the Cherokee which uses the same engine for the same years. 

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Don't forget the Closed Throttle Switch (CTS). Tip of the plunger. Make sure that's functional. 

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37 minutes ago, eaglescout526 said:

You can rebuild the stepper motor. Nickintimefilms on YouTube rebuilt his and it works fine

Why doesn’t he need it? Renix uses it to adjust the speed of the engine at warm up and keeps a decent idle. 

Crown actually makes new units for the Cherokee which uses the same engine for the same years. 

OK. 

 

 

Post link to the Crown. 

 

 

Then unplug it, adjust to idle. 

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I like the "unplug and forget about it" idea. It would be one less part to fail in the future. At that point I would fully remove it and make a bracket with an adjustable idle screw just to get it out of the way. Same with the vacuum lines and wiring. Once the weather gets nicer I plan on eliminating all of the unnecessary stuff under the hood. The truck has not had a consistant idle since I bought it back in Nov., usually between 900-1500 RPM depending on the day. I was dealing with that and not really worried about it, however 3200RPM at idle is far from ok

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6 minutes ago, 90MJ said:

I like the "unplug and forget about it" idea. It would be one less part to fail in the future. At that point I would fully remove it and make a bracket with an adjustable idle screw just to get it out of the way. Same with the vacuum lines and wiring. Once the weather gets nicer I plan on eliminating all of the unnecessary stuff under the hood. 

Once you unplug it it becomes nothing more than an adjustment screw. 

 

 

I don't think this is your problem anyway but this is how you will eliminate it as the source of the problem.

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I am eliminating it either way at this point. Anyone have any advice on vac line rerouting and things I can eliminate while I am at it?

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there's not really anything to remove from the vacuum harness.:dunno:  each thing has a purpose.  I guess you can delete the EGR.  although it's required if you have any sort of visual emissions inspections.

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Update. Unplugged the stepper and turned it all the way in. Idle is now at 1500 with occasional fluctuation to about 1700. It is warming up to go to work at the moment and still not up to temp but at least it isn't racing as high. So now where do I go to get it into the 800 rpm range? We are expecting a heat wave this weekend in the mid 30s so I may wait til then to explore further. Currently its 12 and windy. I've had enough for this morning. Other than vac leaks is there anything else to check out?

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2nd update:

Upon start up when cold I have to pump the throttle like it is carburated since eliminating the idle stepper motor. Once started it idles about 5-600 rpm for a minute or two and then goes to its normal 1500rpm idle, which is still better than a 3200rpm idle, but it just isn't right. With that said, I may reconnect the stepper this weekend and try to find the actual problem. It seems disconnecting it is just a halfassed bandaid to get me back and forth to work this week and not a permanent thing   

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1 hour ago, 90MJ said:

2nd update:

Upon start up when cold I have to pump the throttle like it is carburated since eliminating the idle stepper motor. Once started it idles about 5-600 rpm for a minute or two and then goes to its normal 1500rpm idle, which is still better than a 3200rpm idle, but it just isn't right. With that said, I may reconnect the stepper this weekend and try to find the actual problem. It seems disconnecting it is just a halfassed bandaid to get me back and forth to work this week and not a permanent thing   

Disconnecting it is not a halfassed anything.......it's an evaluation. 

 

Now, you've evaluated. 

 

 

Idle motor is controlled by the ECU, ECU receives information from three sources, temp, AC, and power steering pressure switch. ECU idles-up when AC is on, when it's cold, when the PSPS senses high pressure during a low-speed turn. 

That's what it does. Does the system operate anything what you might be used to in a more modern vehicle? No, it's not nearly as responsive. 

 

 

 

Now that mine works- At cold start- Idle jumps to 1900rpm for 30 seconds, idle comes down to 1100rpm for 30 seconds, then settles down to around 700rpm and remains. 

That's it. 

I did have and do have AC, with AC running idle was unaffected, I replaced PS hose and eliminated the PSPS long ago and again idle was unaffected. 

If your engine is running properly the idle control motor is of little effect. 

 

 

 

What I did was save you $100 and about 2 hours of aggravation only for you realize the stepper motor was not your problem.

 

 

You have to be tech savvy enough and at the same time old-school enough to work through these problems, sometimes it's intuitive and other times it a process of elimination. 

 

 

It's obvious you have a massive vacuum leak. Could be EGR, could be cracked vacuum lines, could be bad/worn TBI...........could be filthy, could be bad temp sensor, could be wiring issues, could be intake/exhaust gasket, could be TBI gasket, could be cracked intake (although unlikely).......you'll have to go through it all. 

 

 

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Check the intake manifolds as Pete mentioned, and inspect these hoses.

 

 

4 cyl TB hoses.jpg

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Ac and power steering are out of the equation since the truck has neither. By halfassing I was referring to disconnecting it and leaving it disconnected as a permanent solution, not as a troubleshooting step 

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Update:

Vacuum lines... replaced every one of them and left the stepper screwed all the way in. Idle is down to about 1000rpm however I have to pump the gas like a carb to start it cold. Fuel pump and filter are new and I am running about 16psi at the TBI. I am happy with it for now but it still is not correct. Planning on cleaning every ground and electrical connection and also the throttle body this weekend. It is a step in the right direction so far.

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