Rough Idle ....

Alright everyone I have a brain teaser I am needing some help with. I have an '01 XJ, cylinder head replaced in July, (thanks all for the help with that). Mid September a rough idle problem started to develop. For a little while once a day, at some point in the day, it would die at a stop sign or signal. But only once and then run fine. A few weeks ago a slight missing sound started :bang: It almost sounds like it is like it is choking. I changed the idle air control valve in May and already confirmed that the valve is not the problem. I have confirmed it is not a bad air filter and all the spark plugs are new as of July's cylinder head job. It sounds like it is not getting enough fuel or air. I am wondering if it might be the Throttle Position sensor or maybe the Ambient Air Temp sensor. :confused: Without having to replace each sensor as I go, any thoughts?

How long since you replaced the O2 sensors?

I have not done it since I bought it back in March 2012. I am not sure it has ever been done. Could a faulty O2 sensor or 2 cause it to do this?

Yes, it is common. When they wear out the fuel air mixture is not right and can affect idle, power and milage.

Are there any ways to tell which is bad or just replace all three?

There is really no way to tell unless they generate a code. But that only happens if the heater fails or there is no signal at all from them. Basically, they need to be replaced every 50K as part of a tune up

I was going to say try O2 sensors.. Would recommend unless you just have a killer discount at a stealership or auto parts store to pick up your O2 sensors through Rock Auto.. Had CEL issues with my gf's LJ and ordered some through AZ and it was crazy high priced.. So I went on Rock Auto and ordered all 4 that hers had brand new NTK O2 sensors, as we figured out that they don't like Bosch sensors, and got all four cheaper then two of the Bosch sensors @ AZ... Just a heads up..

Would a speed sensor cause this problem? I noticed every once in a while my speedometer surges or spikes for no reason and now it is becoming a regular thing.

It could cause it to die if there was a short in it. NW99XJ had that problem a few weeks ago