My CEL just came on a few days ago on my 99' XJ. I have 48K on the clock, it is a second hand jeep to me. The idle gets rough oNLY AFTER the CEL comes on. This happens about every few days. It idles relatively nice the majority of the time it is not. There are some stumbles normally, but not sure whats causing it.

I have new NGK plugs, new wires, rotor (cap is fine) and replaced those about six months ago. This CEL is recent, so I know its not related to the 6mo old parts.

I brought the XJ to Advanced Auto to read the code. The guy brought out his OBD II reader. Nothing....His machine said "No Link". He thought that was strange and brought out another machine at my request, same thing! He said it isn't common and the connector was clean looking with my bright flashlight, what gives?

My friend said O2 sensor, which if it is the original at 148K, I say wow. It lasted a while. I have a Denso one coming (front sensor only for now).

I'm worried about all the extra time and cost or working with a Jeep that can't read codes. Any advise?

 

Well to be honest with you I call bs on there being to codes..maybe try and take it to a autozone or somewhere else.

 

The inability to read codes is either a blown fuse or the pcm taking a dump. Id check the fuses cuz its not likely the pcm stops communicating and still commands injectors and such.

I wholeheartedly disagree that the NGK's are not part of the problem. I know too many people who have started popping misfire codes after switching to them. Sometimes instantly, sometimes a month later.