Can't find this engine miss, help...

[jbossnack]

I just posted these videos on YouTube of my XJ idling cold and then warm:

1. 1999 Jeep XJ - Rough Idle Misfire at Idle - Video 1 - YouTube

2. 1999 Jeep XJ - Rough Idle Misfire at Idle - Video 2 - YouTube

I've got a new pre-cat NTK O2 sensor installed yesterday.
4-pin hole fuel injectors - can hear them firing fine with listening tool (http://www.fiveomotorsport.com/ for stock XJ)
fuel pump module - good pressure on rail Bosch
IAC sensor - replaced Autozone
CPS - replaced Autozone
newer plugs/wires/cap/rotor Champion/Delphi/Brass connections
newer coil - Accel
IAT sensor - replaced Autozone
TPS - replaced Autozone
MAP sensor - replaced Autozone
clean engine oil
all fuses look good
tested lots of circuits with volt meter - found nothing

Ordered a new Coolant Temperature Sensor last night OEM

[Mudderoy]

:welcome: Hey what do you see from the tailpipe when it's missing? Any water vapor (steam)?

[pvt.tadpolxj]

Is there any chance your gasoline is not that good?...xjtalk

[denverd1]

mine didn't have a tailpipe for a while. got one put on for inspection. started hearing the same miss. Although i didn't hear it last time I took it out......

[LizardRunner]

Just to be sure, try doing the paper against the tail pipe test. if it sucks in any at all you have a valve issue. It could also be a valve seal issue since it happens more when fully warmed up. with these out of the way, check for the vapor Muddy mentioned and one other thing I can think of that's out of the norm would be a vacuume leak somewhere.

[jbossnack]

There is a good steady stream of exhaust gas coming out of the tail pipe. It will not suck up the paper so I think the valves are just fine.

There is a lot of moisture coming out the back of the tailpipe. Maybe it's the weather (kinda of humid) but there is a lot of condensation. I think that's good though.

The gas is fine, new, same as in other vehicles I'm using. No problems with them.

I really think this is some sort of 1) vacuum leak or 2) bad sensor

I have checked for vacuum leaks everywhere except for the that thing located in the front bumper passenger side. It's a round ball canister.

Another guy on YouTube says it's the CPS and I need to buy MOPAR only. I have an Autozone CPS, he says they are crap, but I'm not sold on his opinion.

[Mudderoy]

There is a good steady stream of exhaust gas coming out of the tail pipe. It will not suck up the paper so I think the valves are just fine.

There is a lot of moisture coming out the back of the tailpipe. Maybe it's the weather (kinda of humid) but there is a lot of condensation. I think that's good though.

The gas is fine, new, same as in other vehicles I'm using. No problems with them.

I really think this is some sort of 1) vacuum leak or 2) bad sensor

I have checked for vacuum leaks everywhere except for the that thing located in the front bumper passenger side. It's a round ball canister.

Another guy on YouTube says it's the CPS and I need to buy MOPAR only. I have an Autozone CPS, he says they are crap, but I'm not sold on his opinion.

There is a know issue where the harness rests and rubs on the fuel rail near the firewall. Check to see if the harness is resting on the fuel rail. Just use a tie wrap to pull it up and off the rail. The rail rubs through the installation of the "right" wire and randomly grounds it. Probably would manifest as a miss, but have a look anyway.

[3hounds]

Was this issue ever resolved ?

[Cheromaniac]

That surging idle is a classic symptom of a TPS problem. You've recently changed the TPS so it's unlikely that the sensor itself is at fault, but it's not uncommon for the wiring harness connector to the TPS to deteriorate with age and malfunction. Try wiggling the wires to that connector and the connector itself to see if that makes the idle worse (or better). If it does, you've found the problem.
A vacuum leak will usually cause a steady high idle on a speed density EFI engine like the Jeep 4.0 rather than an erratic idle, and a bad CPS usually causes stalling/starting problems.

[modestmar00xj]

im glad you made this post jbossnack! Im having the same exact problem! but i have a 2000 jeep cherokee. im about to do a fuel pressure test on it now and see if the fuel pump because when i turn the key it takes a minute to fire up. but im also going to check out what Mudderoy and Cheromaniac is saying, they gave so good information! Thanks guys!

[Cheromaniac]

I'm having the same exact problem! but i have a 2000 jeep cherokee. im about to do a fuel pressure test on it now and see if the fuel pump because when i turn the key it takes a minute to fire up.

Your problem is different and this might be the reason behind it:

http://www.wjjeeps.com/tsb/tsb_wj_1400201.pdf

Although that TSB is for the '99-'01 WJ, it's also relevant to the XJ.

[3hounds]

Again I ask, was this issue ever resolved ?

Thanks,3