low idle brings periodic stalling

ehall · Aug 22, 2010

For the past few weeks, the jeep has decided it wants a low idle, right at the 500 RPM mark. This is fine except that sometimes it stalls and dies just sitting there. Worst is in gear with foot on the brake and A/C on, but it does it in Park with the A/C off sometimes too.

I pulled the IAC and throttle body, and everything is clean. Seems like the computer just wants a low idle.

One other thing I noticed is that if I goose the throttle a bit after it warms up, then the idle will go a little higher (550-600 RPM) and engine smooths out a bit. I'd like to get idle to setting in that range permanently

Thoughts?

joe_peters · Aug 22, 2010

Is this on your 91 with AW4?

If so, the PCM should be holding your idle, fully warmed up in DRIVE, at 700-750 rpms.

Are you running rich? That would give you a low idle. Or the IAC is not responding to the PCM's retract signals.

Have you tested the TPS?

ehall · Aug 23, 2010

Thanks for the suggestions

ehall · Sep 21, 2010

First, the "low idle" problem was pilot error, IE me looking at the gauges wrong. The XJ idles in park at about 750 just like you'd expect.

Second, the stalling appears to have been be related to the MAP or MAT sensor having a dirty contact. I noticed that the problem was worst when it was really hot outside, so I figured I'd try reseating the air sensors, and the jeep hasn't stalled again since, so there ya go.

cruiser54 · Sep 21, 2010

As you all know by now, I've been a big proponent of refreshing Jeep's grounds, particularly on the Renix era Jeeps as I've had good results. Well, ehall, you've hit upon something else I've come to like as a preventative maintenance/fix for these Jeeps. It's not a bad idea to periodically, or at least when you get a "new to you" Jeep, to unplug about every connector you can see in in the engine compartment, spray it out with contact cleaner, and plug it back in. I prefer DeOx-It which is used on computers and sound boards, but any good cleaner will help. Wouldn't hurt to add a little dab of dielectric grease either. I'm convinced that many components get replaced and the problem gets fixed. But was the component truly bad, or did just the act of unplugging the old and plugging the new one in fix the problem?

joe_peters · Sep 22, 2010

cruiser54 said:
As you all know by now, I've been a big proponent of refreshing Jeep's grounds, particularly on the Renix era Jeeps as I've had good results. Well, ehall, you've hit upon something else I've come to like as a preventative maintenance/fix for these Jeeps. It's not a bad idea to periodically, or at least when you get a "new to you" Jeep, to unplug about every connector you can see in in the engine compartment, spray it out with contact cleaner, and plug it back in. I prefer DeOx-It which is used on computers and sound boards, but any good cleaner will help. Wouldn't hurt to add a little dab of dielectric grease either. I'm convinced that many components get replaced and the problem gets fixed. But was the component truly bad, or did just the act of unplugging the old and plugging the new one in fix the problem?

I absolutely agree with Cruiser54 on this. I would like to add to it a little--pull the CTS and temp gauge senders
(or the combo), and clean the body with some steel wool to remove any scale from it. Pulling and cleaning the MAT wouldn't be a bad idea either.

low idle brings periodic stalling

ehall

NAXJA Member

joe_peters

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ehall

NAXJA Member

ehall

NAXJA Member

cruiser54

NAXJA Forum User

joe_peters

NAXJA Forum User

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