Intermittent stalling (low idle) '96 4.0

[4x4x4x4]

My wife's '96 Sport 4.0 4WD automatic will intermittently stall, evidently because the idle speed does not stay high enough to keep the engine lit. It will re-start readily, and will stay running if I open the throttle a little. I have not noticed any association with engine temperature or humidity. This past weekend, the engine quit multiple times while descending the road to Black Rock Mountain State Park; it's steep, narrow, and crooked -- an "interesting" place to lose power steering.

So far, I'm just throwing parts at it:

> plug wires, distributor cap, and rotor
> throttle position sensor
> idle air control valve

Before I bite the bullet and take it to someone with serious diagnostic equipment, what's your suggestion/guess? Has anyone else seen this problem?

[anaheimxj]

as you are, just throwing out ideas.

>fuel filter
>leak in/around throttle body- too much air into throttle body
>?

[anaheimxj]

>fuel pump
>fuel pick-up in fuel tank

[4x4x4x4]

It probably wouldn't hurt to change the fuel filter, on general principles; however, this doesn't "feel" like fuel starvation. The engine restarts if I open the trottle a tad, and runs fine as long as I don't let it drop to idle.

My hunch is that something is causing the brain to close the IAC valve. But what something? Is possible that the brain is getting a falsely high RPM signal? I haven't noticed the tach doing anything weird . . . except falling to zero when the engine quits.

I replaced the TPS because we had a somewhat similar problem on our '88 4.0, due to the TPS. No help this time, though.

I'm gonna have to buy the FSM.

[themud]

Could be a possible map sensor thats the one on the firewall that the vaccum lines and electrical plug into had my map go out and it was a world of problems....I actually had the same problem on a 91 about 2 years ago never did figure out what it was but I ended up replacing about every sensor one at a time to see if it fixed the problem....One day it was gone on its own (still scratching my head over that one)...you didnt say your milage but you might want to check you O2 sensor and also get you cat coverter flow tested....
luck
themud

[Casper]

I had the exact same problem last week. I replaced the MAP sensor, and YEP!, that did it. So I bet it is the same problem you are having.

Casper

[4x4x4x4]

Y' know, a little voice in my head said "MAP sensor", but I said "Naaaaah." That'll teach me to ignore the voices in my head.

So maybe I'll throw one more sensor at it. On the good side, sensors for the '96 seem to cost about 1/3 the price of those for our late lamented '88.

Thanks!

Any more thoughts?

[4x4x4x4]

We'll monitor this for a few more days, but at this point it looks like the problem may have been the . . . . . . battery?

Friday, the XJ wouldn't start for my wife -- fortunately in front of our house -- going RRrrrr . . . Rrrrr . . . rrr like it had a nearly-dead battery. AutoZone confirmed a croaked battery. With a new battery, it starts fine and the intermittent stalling seems to be fixed . . . so far. With an intermittent problem, y' never know.

I think the battery had a bad internal connection: sometimes yes, sometimes no. I'm guessing that when the battery hiccuped while running, it tricked the injection. I reckon we're pretty lucky, because that sort of problem has been know to blow-up batteries.

How odd. I'll let you know if the stalling problem stays fixed.

Thanks for all your suggestions.

[Matthew Currie]

The battery paroblem is not that strange, really. I've seen similar problems when a battery gets bad, because one of its functions is to stabilize the voltage to the ECU. The output from the alternator is pretty dirty, and although you can start and run a vehicle with even a stone-dead battery after a boost, it will run badly because it's really running off the alternator rather than the battery. Some ECU's just won't work right with a bad battery, and Chryslers seem to be among them.

[JstSurrender]

I seem to be having a similar problem to this. Although it's never died while running. This morning it was at the point of stalling but was trying to keep running, as I stepped on the gas I didn't receive any response. I simply turned the key off, and restarted it, opened up the throttle to keep it running then I was fine.

I had a couple questions, What is the ECU and FSM?

~Scott