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Constantly Needing to Reset PCM - IAC Valve Issue?

TheSloMoShow

NAXJA Forum User
Location
Columbus,OH
Good morning everyone,

I've been having an issue with the truck getting started, and maintaining idle as of recent.

About once or twice a week, I can't start her up. The starter cranks and the engine nearly gets going but then it just dies. I can give it gas, but as soon as I leave off the pedal it dies.

There are other times where I'll notice that when coming to a stop that if I completely leave off the pedal, it'll die too and/or have a really weak idle.

No CELs ever come on in any case.

My original thought is that it has to be the IAC valve, since it happens when I'm off the pedal and it seems like it can't get enough air.

I've replaced the part with OEM within the last month fyi.

Also, to get it working again each time I reset the PCM but somehow the issue still arises a couple days later and I can't figure out why. If simply resetting the PCM gets it working, I can't imagine it's an issue physically with the IAC valve itself or the wiring harness/connector, but then I don't know where to look next.



Anyone else encounter this issue?
 
any codes?
Never, that's what I find odd.

I was leaning towards replacing the harness connector as one of these spade connectors popped out recently. I'm thinking maybe it isn't making a good connection.

But if the truck works after resetting the PCM, without me altering connector, then I don't think it's an issue with any of the spade terminals.
 
.... having an issue with the truck getting started, and maintaining idle as of recent.

.... starter cranks and the engine nearly gets going but then it just dies. I can give it gas, but as soon as I leave off the pedal it dies.

There are other times where I'll notice that when coming to a stop that if I completely leave off the pedal, it'll die too and/or have a really weak idle.

Those are the symptoms of low battery voltage.

For 1996+ Jeeps, the OBD-II engine computer (ECU/PCM) re-boots, and the idle settings are deleted, when you: (1) let the battery run down by leaving the lights or radio on, (2) disconnect the battery for an extended period of time, (3) when the battery goes bad and needs replacing, (4) when the alternator is not properly charging the battery, (5) or when poor battery connections result in a voltage drop at the PCM or poor battery charging. Loose, corroded, or damaged battery cables or ground wires may also cause or contribute to the problem.

A faulty Coolant Temperature Sensor may also cause similar symptoms. Testing of the CTS is recommended as part of the diagnostics. A poor ground at the ignition coil can also cause similar symptoms.

The reboot symptoms are: (1) having difficulties starting the engine without depressing the gas pedal, and (2) the engine will have a low idle and probably stall unless you keep your foot on the gas pedal. (3) The ECU will relearn the idle settings after a short period of driving, and the engine will sometimes start and idle normally.

Begin with basic trouble shooting of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables or connectors and replace as needed. Copper wires should be copper color, not black or green. Do the same for the grounding wires from the starter to engine block, the ground wires at the coil, and the ground wires from the battery and engine to the Jeep's frame/body. You must remove, scrape, and clean until shiny, the cable/wire ends, and whatever they bolt to. Jeeps do not tolerate low voltage, bad connections, or poor grounds.

If the symptoms reoccur, you need to have your battery and/or the alternator Load Tested at a repair shop or auto parts store. This is usually a free service they offer to bring in potential customers. Handheld testers are very inaccurate and will usually pass marginal alternators. Even with low battery voltage, the engine will start, but the ECU can re-boot multiple times and a new battery may be required.

Cleaning the Idle Air Controller (IAC), regular tune-ups, and using fuel injector cleaner should be part of your routine preventative maintenance for smooth starts.
 
Those are the symptoms of low battery voltage.

For 1996+ Jeeps, the OBD-II engine computer (ECU/PCM) re-boots, and the idle settings are deleted, when you: (1) let the battery run down by leaving the lights or radio on, (2) disconnect the battery for an extended period of time, (3) when the battery goes bad and needs replacing, (4) when the alternator is not properly charging the battery, (5) or when poor battery connections result in a voltage drop at the PCM or poor battery charging. Loose, corroded, or damaged battery cables or ground wires may also cause or contribute to the problem.

A faulty Coolant Temperature Sensor may also cause similar symptoms. Testing of the CTS is recommended as part of the diagnostics. A poor ground at the ignition coil can also cause similar symptoms.

The reboot symptoms are: (1) having difficulties starting the engine without depressing the gas pedal, and (2) the engine will have a low idle and probably stall unless you keep your foot on the gas pedal. (3) The ECU will relearn the idle settings after a short period of driving, and the engine will sometimes start and idle normally.

Begin with basic trouble shooting of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables or connectors and replace as needed. Copper wires should be copper color, not black or green. Do the same for the grounding wires from the starter to engine block, the ground wires at the coil, and the ground wires from the battery and engine to the Jeep's frame/body. You must remove, scrape, and clean until shiny, the cable/wire ends, and whatever they bolt to. Jeeps do not tolerate low voltage, bad connections, or poor grounds.

If the symptoms reoccur, you need to have your battery and/or the alternator Load Tested at a repair shop or auto parts store. This is usually a free service they offer to bring in potential customers. Handheld testers are very inaccurate and will usually pass marginal alternators. Even with low battery voltage, the engine will start, but the ECU can re-boot multiple times and a new battery may be required.

Cleaning the Idle Air Controller (IAC), regular tune-ups, and using fuel injector cleaner should be part of your routine preventative maintenance for smooth starts.
Thanks.

I refreshed the ground wires tonight, will try that to start to see if something small and minute.

What I'm still not understanding is if it's possibly an issue with low battery voltage, why resetting the PCM is the temporary cure?

I would think resetting the PCM should have no effect if the root cause is low voltage.
 
Well, I went back out to 'Check my Math' and possibly found the culprit.

The picture below isn't mine, found it of the net, but 1 (the fatter wire) of the 3 ground wires shown here wasn't connected on my block. I connected all 3, hopefully this does the trick

1efe7839587da2991ca18dd479bd267a.jpg
 
That will also cause issues.


As I understand the process, re-setting the PCM replaces any learned data, with pre-programmed average generic data.

A re-boot due to low voltage or interrupted voltage deletes any learned data, and does not replace it with anything, thus the hard start, low idle, and stalling.
 
Well day one down, and no issue. Fingers crossed tomorrow is the same. This issue usually occurs after truck sits all night, so we'll see how tomorrow morning goes.
 
im having a similar issue on my 97 country. I just had the remote start guy hookup the rear defroster which he failed at. the jeep ran great when i dropped it off and terrible ever since at cold start. low idle, stalls unless gassing at start.but when warms up after driving idles good. even with new mopar iac. Im leaning towards ecu replacement but would like to test wires first. Ive been searching for the pin charts from ecu to iac.
 
ECU problems are last on the list of possible suspects and should only be considered after a logical and thorough diagnostics of the usual suspects. I would suppose the rear defrost was disconnected because it has a short or other fault and was draining the battery.
 
it works again thanks to me. It worked when i dropped it off. i wanted it on the trunk button of the remote start to activate the defroster only when i wanted to. I got the jeep back with a CEL and the defroster didnt work. I unhooked the relay he wired into it and changed the fuse ad relay in the vehicle. Restoring it to factory working order. But the 0505 code keeps coming back
 
has yours been better since the ground issue fix?
It has. I haven't had any issues with starting up and stalling since I cleaned those grounds. It's hard to day that this 100% cured it, because as you know electrical gremlins can manifest themselves in many ways. But for the time being, it's worked. If the issue pops back up for me I'll note it here because then obviously I need to look elsewhere.
 
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