My 2000 misses badly when the temp is between cold and warm. It runs fine when you first start it, and it runs fine after it is completely warmed up, but just before it is warmed up it will barely stay running. Any thoughts on what might be wrong? Several times I have had to drop it in neutral and rev it up just to keep it running.

 

Temp sensor? O2 sensor?

 

ok, I will have to check those. Do you know if there is a way to test them without just replacing them?

 

I agree with Gee oh Dee that the coolant temp sensor and the oxygen sensor(s) are possibilities.

Have you ever seen a check engine light? Even if the answer is no, I would get a code reader or a scan tool on your computer and see if there are any "stored" or "pending" codes. These codes are invaluable in troubleshooting.

The coolant temp sensor can be tested, but to accurately test it is kind of involved; involves a beaker of heated water and a calibrated thermometer and checking resistances. You can take a quick gut check of resistances with the sensor still installed and that usually tells the story, but isn't 100% fool proof. With the cost of this sensor being pretty low, most guys just swap them out. Located on your thermostat housing.

Oxygen sensors too can be tested but not easy if you haven't ever done it before. If sensors have between 125k and 150k on them and they are suspect, replace them with new NTK sensors. Stay away from ebay sensors UNLESS the brand name is confirmed and never, ever buy oxygen sensors that are not an exact fit for your vehicle.

This does not sound like a spark plug issue, but how many miles are on yours?

 

The jeep has 160,000 miles on it. Not sure how old the plugs are, we just got the jeep. So, would you start with the temp sensor or the O2 sensors?

 

With a "new-to-you" 2000 XJ, I would start with 6 new NGK copper plugs gapped to .035 (you should change them so you have a known baseline for future maintenance)

Then I would check the computer for any stored codes.

If there are no codes, I would then consider the temp sensor and fresh oxygen sensors.

 

Ok, I will try new plugs, right now it has no engine codes. Though it does have an airbag light on. LOL, but I hear that is almost normal for an XJ.

 

Just because the CEL isn't lit up doesn't mean you don't have codes stored.

 

Hmmm, I didnt know that. I thought as soon as a code flashed it turned the light on.