93 XJ runs rough for first 1/2 mile of driving ???

Symptoms:

-after start up when warm or hot, has happened when cold
-usually idles just fine directly after start up
-initial acceleration, if more than slight, will induces missing and bucking
-WOT will run normally, and is sometimes the only way to accelerate
-idle will sometimes be rough for a minute, but it corrects itself and don't stall
-symptoms disappear after a minute or 1/2 ablock of driving or so, usually faster with WOT
most of this is copied from another thread and seemed to be a "fuel line check valve", does my 93 have one ?

It feels like your letting the clutch out with little or no gas pedal, but like I said before it's gone in a minute or by the time I get to 3rd than it's fine until it sits for 30min to an hour.

I do have a "21" code = 02 sensor and I will be grabbing one this week (when time allows it) but will that really cause this kind of issue ???

I took off TB and cleaned IAC, and TB and replaced gasket, new wires, plugs. The dist cap is only 12k old I also ran some MMO through it and new gas. Does this sound more like a TPS,CPS, the O2 or just fuel filter ???

I have drove jeeps for years (ZJ's and WJ's) this is my first XJ and I love it!
So I'm new here but not to JEEPS!!!!!
Ive been a member @ JF for several years but seem to be more XJ help here vs there.....

Thanks guys

The fact that you have a code AND symptoms is probably not coincidental. Especially if both came on at approximately the same time. Did they?

Gotta chase and resolve that code 21; that is absolutely job #1.

21 means neither rich or lean is detected from oxygen sensor input. How old is your oxygen sensor? They have a finite lifespan of between approximately 100k and 150k,
depending on the efficiency of the engine.

Consider replacing it; they're not that expensive and it could very well be root cause here. I prefer NTK for 91-01 4.0 engines.

I just bought this thing, it was dealership maintained by the last owner and not sure before that. It was pretty well kept and I still have great gas mileage. The sensor looks pretty new but that really don't mean anything.
The XJ has 136k on, I pretty much have an OCD with maintenance so the sensor would have been part of my normal parts list for a new to me jeep.

I am ordering one now.........

I just can't grasp that if it was the o2 sensor u would think it would act up all the time.......:dunno:

Only one way to find out........and that is to get that new sensor in there.

Stay away from no-name flea bay stuff and anything universal. Lots of junk O2 sensors fors sale out there.

NTK is the OEM supplier to Jeep and has been for a while; that is why I recommend them.

A vacuum leak....is possible you have a cracked exhaust/intake manifold gasket or a cracked exhaust manifold.

I think I do here a bit of a leak at the back of the header.......

birchlakeXJ said:

Only one way to find out........and that is to get that new sensor in there.

Stay away from no-name flea bay stuff and anything universal. Lots of junk O2 sensors fors sale out there.

NTK is the OEM supplier to Jeep and has been for a while; that is why I recommend them.

Click to expand...

every local parts store is out of NTK brand (welcome to my world !), they have denso and bosch in stock........

Ok I definitely have a "small" leak either in header gasket or else its the infamous cracked header. I popped the hood this AM while it was cold and I could see some exhaust trickle up from by the firewall, the jeep is not loud at all and get still gets great MPG!!!!

will this create a code "21" for an o2 sensor, and my hesitation ???

I have been driving my ZJ and WJ, the past few days until I get my sensor and some other maintenance stuff in the mail.

wsar10 said:

I just bought this thing, it was dealership maintained by the last owner and not sure before that. It was pretty well kept and I still have great gas mileage. The sensor looks pretty new but that really don't mean anything.
The XJ has 136k on, I pretty much have an OCD with maintenance so the sensor would have been part of my normal parts list for a new to me jeep.

I am ordering one now.........

I just can't grasp that if it was the o2 sensor u would think it would act up all the time.......:dunno:

Click to expand...

The ECU will try to use the O2 sensor data at first. If the ECU determines that the data is causing miss fires, i.e. bad O2 sensor data, the ECU will switch to open loop operation and ignore the O2 sensor. If the O2 sensor is not getting 12 volts to the sensor's internal heater (the second pair of wires) the O2 sensor will be slow to warm up, and will give out bad data until it is hot enough (from exhaust gases) to work right (WOT will get it hot faster). With out the internal electric heater in the O2 sensor working, the O2 sensor gets too cold at extended idle and will cause a miss. Either power to the heater can be missing, or the heater can be burned out in the sensor, but the O2 sensor could still be working while driving.

wsar10 said:

every local parts store is out of NTK brand (welcome to my world !), they have denso and bosch in stock........

Click to expand...

Bosch made the original Renix and OBD-II oxygen sensors. I was told they invented and patented the original O2 sensors. I run the Bosch O2 sensors on my Renix jeeps.

update:

Got the XJ out this weekend and threw an O2 sensor at it (finally had time) and so far the hesitation is gone ! I'm gonna drive it this week to be sure, and we have a header replacment scheduled in 2-3 weeks.