DDJeep1996

I'm having issues after driving after about a half an hour or so. I'll pull up to a stop and if I sit for a few seconds the rpms will drop and stall, or stumble and return to normal. While driving I will get a hesitation that scares the crap out of me and then back to normal and this will usually only happen once. Jeep has 117,000 miles and is in very good condition otherwise. I've tried to diagnose the problem with no luck. So far I've replaced the following:
IAC Valve (Aftermarket)
TPS Sensor (Aftermarket)
CPS Sensor (Mopar)
Cap(Duralast), Rotor (Duralast), Champion Copper Plugs (gapped at .35), and Taylor 8mm Plug wires
Felpro Valve cover gasket (tired of drips in the driveway)

All sensors had never been replaced before. I've looked for vacuum leaks and can't find any. Am I missing something? I don't want to throw any more parts at it. Anyone have any advise?

jordan96xj

If your 96 supports OBD2 I would -highly- recommend getting a OBD2 scanner so that you can see what your computer is seeing. It can be immensely helpful for intermittent problems like this.

Given all of the sensor replacements that have already happened. I would next want to see what the O2 sensors and fuel trims are doing.

Are you able to keep it from stalling by feathering the gas pedal while it is happening?

DDJeep1996

I have OBD1. Should I take it to autozone or similar to have them scan it? I have no check engine light. If I put the jeep in neutral and just a little touch of the gas pedal it won't stall.

jordan96xj

Ok. If it is OBD1 autozone may not have a scanner that can do it. They typically just have their off-the-shelf OBD2 scanners to work with.

But from what you just said, a stall at idle that can be counter-acted with just a little touch of pedal is a strong indicator for an IAC problem.

DDJeep1996

Maybe I got a bad IAC from the store. It was an aftermarket one. Maybe I should try a Mopar one?

jordan96xj

Like with any of these types of parts, there is quite a wide range of price and quality. I put a Standard Motor Products IAC on mine 2 years ago and it has about 40k trouble-free miles on it. I don't think a Mopar IAC is a must-have (as it is not a sensor, and doesn't measure anything). But if you can get a Mopar one at a reasonable price, certainly that could be good too.

OldTires

Check your grounds, battery cables, sensor wires and all. You can park it, idle it, and then open the hood and start wiggling the wires. See if you can recreate the issue. This includes the PDC module.

DDJeep1996

I'll give that a try when I get home today.

DDJeep1996

So I tried this yesterday and I couldn't recreate the issue. I also installed a new Mopar IAC. I'm still having the same issues. What else could be causing my problems? I physically checked for vacuum leaks, should I do a vacuum test? I've never had to do one, I've seen the propane test and smoke test. Could it be a upstream O2 sensor?

jordan96xj

Yes, it could be the upstream O2 sensor. (but that doesn't mean it is the only thing it could be).

If I didn't have the ability to scan the computer and see what it thinks is happening, I would want to measure the voltage from the upstream O2 sensor, to see if it is doing something other than what it should.

DDJeep1996

I don't own a scan tool and have never used one. Would using one help diagnose my issues? Are they pretty straight forward to operate and understand? Is there a certain one you could recommend?

Cummins93

Are you sure your 96 isn't obd2? If it's the JTEC ecu (3 plugs ) it should be.

jordan96xj

For XJs with OBD2, scan tools are very cheap (I think they should be must-have items in your go/tool bag). But for OBD1, it won't be so easy or cheap.

What I was saying was that if I did NOT have a scan tool, I would take a multimeter and try to ensure that the upstream O2 sensor is traversing its normal range of .1-.9 volts (repeatedly). But not all meters can do this well because they tend to measure the voltage infrequently and then average the values. But if you watch it long enough, you would see whether it is "stuck" at a low (near .1) or high (near .9) voltage. This would indicate that it is probably causing the computer to run constantly rich/lean and may contribute to the problems you are seeing.

awg

If you dont mind me asking, how do you know you have OBD1 ?

Does your vehicle have an OBD2 port under the dash, near your knee (a trapezoid shaped female connector, with about 20 pins)?

You have not mentioned the ignition coil, is it visibly cracked?..remove and examine it, not expensive to replace

my 3 X '96, have every indication of being OBD2, read OBD2 codes with my 15yr old code reader

however, I bought a "Torque" bluetooth code reader, very common, $20 works with your phone, plugged it into my OBD2 port...and IT says I have OBD1 ??

oval brass ID plate on firewall says 4/96

I used the "Torque" OBD2 reader to diagnose & repair a failed coil-over-plug on a later model vehicle ystday...great little tool

DDJeep1996

I was told that the 96 year was set up like OBD2 under the dash (which I have) but still used OBD1 codes. Was I misinformed? How could I find out for sure which one I have? I have not checked the ignition coil.