Stalls, low idle...

Started yesterday, when I stop it stalls (traffic lights, stop signs, driveway etc. etc.). About a week ago I had a strange incident with the battery guage when it dropped to zero while my MM said 13volts and then just went back to normal. Anyway I was just driving the other day and I came to a light, stopped and the RPMs dropped to nothing, no previous issues, nothing leading up to this, just out of nowhere on my way home. Starts without issue but RPMs immediately drop if it is not tached up. Once it gets going I'm fine until I come to a full stop again. It seems odd because the RPM's immediately drop on only the backwards movement of the stop, so long as the vehicles weight is in forward motion, however slight, everything is fine. I tried some new gas, we'll see where that goes when it mixes with the 7 or so gallons I had left. I just finished a 150mile trip yesterday with no issues at all, highway speeds up to 80 ish, stopped in traffic on I-95 for a while, even parked on the side of the road running for 45 minutes, no probelms at all. Also, it seems to get better with more driving but after it sits for a while I can't even safely back out of my driveway. I'm lost, dealership on monday it looks like...
Thanks as always,
Alex

What year, model, pedigree??/

It sounds like it might be a ground issue at the passenger side of the engine block, or battery ground, or both, if it wasn't just a bad fuel problem.

Try to be a bit more specific, step by step detail, chronolgically, you have good detail but I get lost in the timing of what happened exactly when, and when it stopped?

IAC motor maybe.

Kyung

OK, sorry...
2001 Sport, mains replacements...nothing modified recently.
1)2 Weeks ago Battery guage fails, then comes back within 1 hour, no abnormalities since.
2)Yesterday 150 Mile trip, mostly highways, some stop and go. No Issues.
3)Today (4/7) On my way home in town I stopped at a light and it stalled out and has had those problems that I described since.
4) Currently I am able to run, but when I do stop I get an idle at about 0250 instead of it just stalling and it occurs at the times described above.
No history of issues, battery puts out ~14VDC (Optima YT)
I have two 7 cell blue tops in the back on an isolator, with them disconnected the issue is the same.

EMSJEEP said:

OK, sorry...
2001 Sport, mains replacements...nothing modified recently.
1)2 Weeks ago Battery guage fails, then comes back within 1 hour, no abnormalities since.
2)Yesterday 150 Mile trip, mostly highways, some stop and go. No Issues.
3)Today (4/7) On my way home in town I stopped at a light and it stalled out and has had those problems that I described since.
4) Currently I am able to run, but when I do stop I get an idle at about 0250 instead of it just stalling and it occurs at the times described above.
No history of issues, battery puts out ~14VDC (Optima YT)
I have two 7 cell blue tops in the back on an isolator, with them disconnected the issue is the same.

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I am not an expert on the newer models, but there some similarities so I would start by looking for a loose or corroded, or oily, poor ground at the battery or one of the main engine or firewall grounds under the hood. Follow the large ground wires from the battery to the engine block, on the older models it is near the dipstick on the passenger side and is notorious for your kind of problem. Also check for loose fuses in the Power Control center, (under the hood on yours I think?).

If it was just an idle problem I would say the IAC is the problem. If it was a variable idle, or sensitive to foot position on the gas peddle (bouncing around with small movements of the gas peddle) I would suspect the TPS. But with the battery guage issue, plus the low idle my experience says it is a poor ground in the sensor, computer, controls, and battery ground circuit, and jeeps are notorious for this problem. A slightly loose, dirty, oily set of ground sensor, control, computer & battery contacts stacked in one spot near the oil dip stick with shifting ground continuity can cause all sorts of strange effects. You have seen two of them!

With a little luck you won't need any parts, just some solvent and scotchbrite. Be sure to clean the battery cables and posts as well!

Not familiar with the "two 7 cell blue tops", is that an extra set of batteries for auxiliary stuff?

Also, no starting problems and 14 volts says the battery and alternator should be OK.

Ecomike said:

Not familiar with the "two 7 cell blue tops", is that an extra set of batteries for auxiliary stuff?

Also, no starting problems and 14 volts says the battery and alternator should be OK.

Click to expand...

They are 7 Cell (not 6) Optima Blue Tops, the marine grade "house" batteries. Disconnected or connected the problem is the same so I don't think they have anything to do with the issue.

Thanks for your help, I'm going to check out the grounds now. They were all pretty well protected when I redid the mains in 2ga. but we'll see, thanks again!

The "battery guage when it dropped to zero while my MM said 13volts" problem sounds like an intermittent short or loose connection somewhere. The rest sounds like an IAC hanging up.

Have you tried cleaning and relubing the IAC?

But the IAC would not cause the battery gauge and lower voltage (13 versus 14 volts ) issue. Is the serpentine Belt and tension OK?

This is going to sound realy stupid, but it happened to me. Jeep(2000 sport in my case.) suddenly starts idling slow and stalling out. It stopped when I replaced the battery. Old battery had plenty of juice to turn the engine over, and never noticed any elec. problems. Apparently the computer is sensitive to BATTERY voltage, not system voltage.

tbburg said:

This is going to sound realy stupid, but it happened to me. Jeep(2000 sport in my case.) suddenly starts idling slow and stalling out. It stopped when I replaced the battery. Old battery had plenty of juice to turn the engine over, and never noticed any elec. problems. Apparently the computer is sensitive to BATTERY voltage, not system voltage.

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Battery volatge affects system volatge. Also you might have replaced poor post electrical connections by replacing the battery! Just cleaning the posts and cable ends might have done the same thing! But yes, batteries can do weird stuff just before they die.

IAC Motor it is!

So, where is the IAC motor and what does it do exactly? Replaced by the shop for $250 :banghead: so many better things to do with $250...

EMSJEEP said:

So, where is the IAC motor and what does it do exactly? Replaced by the shop for $250 :banghead: so many better things to do with $250...

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It's mounted on the side of the throttle body. The PCM uses it to control idle speed and start up flare by letting some air around the closed throttle plate. If you look into the throttle body you will notice a little opening above the plate. That passage ends below the plate. The IAC controls the amount of air that passes through that passage.

Kyung

Gotta love the stealerships repair departments. It costs about 60 to $70 at local non-OEM parts houses and takes about 10 minutes to replace, or 5 minutes if you have done it before.

$148 for the part, about $80 for labor, I think it took them a while to find maybe...who knows...