I've officially found the most unsolvable idle issue...

Alright guys this might get a little long, but bare with me. I've officially found the strangest idle/performance issue that I can't find the fix for. Pictures and videos ahead.

1997 Cherokee Sport

P.s. I feel like this belongs here in OEM tech since it's engine/electrical related; even thigh my jeep is far from stock. Mods, feel free to move it if need be.



What it's doing:

Alright, here it goes. The way my engine is idling is odd. When I first start it up, things are gfineand dandy. It gets up and goes just fine, and the idle is mostly regular. However, when I turn it off and start it up every time after, my idle gets lower and lower and worse each time. The lowest I've seen my tachometer read is a steady 250 RPM, which is usually after two or three starts. Along with this, it "hunts" while at idle no matter what. And when driving, it gets sluggish and I lose gas mileage. Here's a video of what I mean (idle):

https://drive.google.com/file/d/0B4TZ-9zFmzyaSTl6cDhKRW9sbWM/view?usp=drivesdk

Naturally, I suspected it is the TPS

It exhibits all the symptoms of a bad TPS, including transmission shift points being affected. Yet upon replacing, that doesn't fix it.

Which leads me to believe it's something to do with wiring going into the injectors. So I tested voltage going into my injectors with a probe and recorded the screen as I revved the engine to show what the multimeter says:

https://drive.google.com/file/d/0B4TZ-9zFmzyaOWNYd00tT28tYVE/view?usp=drivesdk

As you can see, when it's at idle, the volts are all over the map. When I rev, the volts are still a little screwy. When I let go, the engine/voltage drops extremely low in RPM, nearly stalls, and comes back to life, sorta. I'm not sure if the voltages are correct so if you know something I don't, let me know!!

Here's how I had my multimeter connected to test the injectors:

https://drive.google.com/file/d/0B4TZ-9zFmzyaZ2ZZMGxDUnZqaXc/view?usp=drivesdk

https://drive.google.com/file/d/0B4TZ-9zFmzyaWDRfZEtpeGdTMjA/view?usp=drivesdk

I simply just used an in line pokey-stabby head to get measurements.


Final Issue: when I let it idle for a while, it starts to do this horrible, violent stumbling type thing and my air intake starts to sound like a jet engine. I have no idea where this comes from:

https://drive.google.com/file/d/0B4TZ-9zFmzyaaWZSOWZOM0dSYVk/view?usp=drivesdk


Finally, I've narrowed it down to a handful of things. In order it goes:

- Engine wiring harness
- Timing
- Spark related issue

If someone can give me a wiring diagram to the injector end of the PCM that includes ohms and voltages for a 1997 Cherokee Sport that'd be absolutely fantastic. I hope i put enough detail in here. I'll be cross posting it to multiple forums. Thanks all, stay radical y'all

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I may be able to find you that wiring when I'm at work tomorrow. I'll post what I can find for you

xCWolf said:

I may be able to find you that wiring when I'm at work tomorrow. I'll post what I can find for you

Click to expand...

Thanks man, preferably w/ voltages and ohm ratings and where to put the multimeter leads to properly test. Blah blah, all that stuff. I appreciate it!

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I'll PM you what I have, I'de be pulling it from AllData and/or directechs

Also I can't see your black/com lead where do you have it hooked up?

xCWolf said:

Also I can't see your black/com lead where do you have it hooked up?

Click to expand...

I'm running them both in line with both injector wires running in and out of the back end

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xCWolf said:

Also I can't see your black/com lead where do you have it hooked up?

Click to expand...

It's under the red lead in the first photo

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Off the top of my head the video you have for the injectors meter reading looks pretty accurate. I'll see what I can pull up too

xCWolf said:

Off the top of my head the video you have for the injectors meter reading looks pretty accurate. I'll see what I can pull up too

Click to expand...

Thanks again man, I'm about to start banging my head against a wall figuring this out. I'll check timing later tonight or tomorrow while I wait on a response from you with diagrams. Thanks again

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Are you installing genuine Jeep parts, or crappy Chinese "Lifetime Warranty" parts ?

Test the TPS and inspect/test the wire harness continuity. The Idle Air Controller is in charge of the idle speed, clean it and the throttle body, test it, and test the wire harness continuity. A unexplained drop in gas MPG's of 30-40% is usually a faulty O2 sensor and/or a cracked exhaust manifold. Again, testing and physical inspection is necessary.

You should also test/inspect the battery and alternator and test/inspect/clean/snug all the battery/alternator/ground wire connections and wires. Low voltage will reboot the PCM and idle settings are deleted. Low voltage while driving can mess with the PCM and cause odd symptoms.

Tim_MN said:

Are you installing genuine Jeep parts, or crappy Chinese "Lifetime Warranty" parts ?

Test the TPS and inspect/test the wire harness continuity. The Idle Air Controller is in charge of the idle speed, clean it and the throttle body, test it, and test the wire harness continuity. A unexplained drop in gas MPG's of 30-40% is usually a faulty O2 sensor and/or a cracked exhaust manifold. Again, testing and physical inspection is necessary.

Click to expand...

Parts are genuine, also I did all of that already. Except look into o2 sensors and check continuity. I'll check those in the morning, thanks for the suggestions

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Can anyone explain the stumbling and jet engine sounding air intake? That's odd to me

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Sounds like a massive vacuum leak on the noise, but that should cause a high idle. I had an O2 sensor wired backwards once it wanted to idle at 250 rpm.

What all have you already done? Plugs, wires, gas leak at the FPR check, gas pressure while running!!!!!!

What kind of work did you do on it before the problem started?

Ecomike said:

Sounds like a massive vacuum leak on the noise, but that should cause a high idle. I had an O2 sensor wired backwards once it wanted to idle at 250 rpm.

What all have you already done? Plugs, wires, gas leak at the FPR check, gas pressure while running!!!!!!

What kind of work did you do on it before the problem started?

Click to expand...

Hmmm, you might bff onto something. I'll check all this tomorrow

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Also sorry for typos, I'm real tired

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I have no idea about your voltage issues. One thing that may be helpful is to put your meter on a low DC voltage scale and measure for voltage between an injector and a TPS ground to the battery ground. This is a quick test for the general health of our ground circuits. There should be zero volts, any volts (more than a fraction) means you have a ground issue.

I had a ground wire on that circuit that was just sitting in an uncrimped splice. My idle was all over the place. I eventually shook the harness at just the right time and found the fluctuation on my meter.

Is your EGR still hooked up? Not electrical, but if it is acting up it can really mess with your idle. Also have a close look at your EGR solenoid plug, they tend to disintegrate over time. The default for the solenoid is open, if power is interrupted the solenoid will open and actuate the EGR at the wrong time (low RPM's). If the diaphragm is broken on the EGR it can whistle.

Just a few ideas.

8Mud said:

I have no idea about your voltage issues. One thing that may be helpful is to put your meter on a low DC voltage scale and measure for voltage between an injector and a TPS ground to the battery ground. This is a quick test for the general health of our ground circuits. There should be zero volts, any volts (more than a fraction) means you have a ground issue.

I had a ground wire on that circuit that was just sitting in an uncrimped splice. My idle was all over the place. I eventually shook the harness at just the right time and found the fluctuation on my meter.

Is your EGR still hooked up? Not electrical, but if it is acting up it can really mess with your idle. Also have a close look at your EGR solenoid plug, they tend to disintegrate over time. The default for the solenoid is open, if power is interrupted the solenoid will open and actuate the EGR at the wrong time (low RPM's). If the diaphragm is broken on the EGR it can whistle.

Just a few ideas.

Click to expand...

I'm about to start using these suggestions so I'll report back later tonight if I find anything guys, stay rad

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First thing that came to mind is the MAP.

Wouldn't an open EGR (error) and a working O2 sensor make the ECU add fuel and raise the idle speed? Thus running the engine rich (smell at the exhaust), with the O2 running lean, but the engine actually running rich?

Never gave the EGRs much thought, never had a bad one since I had a 78 Dodge, and when it went bad I could smell the carburetor side of the EGR rubber hose smoking like crazy, it stunk, and was easy to diagnose. but your comments have me thinking. Never read of a confirmed issue cause by an EGR here except yours. Not even a failed tailpipe issue that I recall. But I see your point, has me thinking now.

8Mud said:

I have no idea about your voltage issues. One thing that may be helpful is to put your meter on a low DC voltage scale and measure for voltage between an injector and a TPS ground to the battery ground. This is a quick test for the general health of our ground circuits. There should be zero volts, any volts (more than a fraction) means you have a ground issue.

I had a ground wire on that circuit that was just sitting in an uncrimped splice. My idle was all over the place. I eventually shook the harness at just the right time and found the fluctuation on my meter.

Is your EGR still hooked up? Not electrical, but if it is acting up it can really mess with your idle. Also have a close look at your EGR solenoid plug, they tend to disintegrate over time. The default for the solenoid is open, if power is interrupted the solenoid will open and actuate the EGR at the wrong time (low RPM's). If the diaphragm is broken on the EGR it can whistle.

Just a few ideas.

Click to expand...

Ecomike said:

Wouldn't an open EGR (error) and a working O2 sensor make the ECU add fuel and raise the idle speed? Thus running the engine rich (smell at the exhaust), with the O2 running lean, but the engine actually running rich?

Never gave the EGRs much thought, never had a bad one since I had a 78 Dodge, and when it went bad I could smell the carburetor side of the EGR rubber hose smoking like crazy, it stunk, and was easy to diagnose. but your comments have me thinking. Never read of a confirmed issue cause by an EGR here except yours. Not even a failed tailpipe issue that I recall. But I see your point, has me thinking now.

Click to expand...

Hmmmmm, I'll give it a look

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