ecksjay00

What is considered to be a normal idle range for the XJ? Not specifically where other member's XJs typically idle, but rather, what is the normal rpm range at idle? For example, my 2000 XJ 4.0 idles at about 650-700 rpm in park, about 625-675 rpm in drive (per OBDII Bluetooth scanner). I ask, because I am trying to solve a vibration issue I have in both idle and park and wondered if this range (i.e., bouncing between 650-700 rpm while in park) was wide enough to cause my vibration issues. I have no issues with driving, getting up to highway speeds, no hesitation, no stalling, etc. Just an annoyance really, but I'm not sure if this is a typical annoyance or indicative of something else needing attention. Has had a recent tune up in last 7000 miles (new Champion copper plugs, new coil rail), new Clearwater cylinder head, head gasket, and intake gasket replaced, fuel injectors cleaned, fuel pressure checked and ok. IAC cleaned, then another IAC from a donor was put in - no change. Checked for vacuum leaks with starting fluid and propane - nothing found. Motor mounts seem to be fine, they should have been replaced when the PO replaced the engine about 12,000 miles ago. They do appear to be Mopar mounts, so maybe they reused the old ones or did it right and went OEM? Transmission mount looks like it may need replaced, but I don't think this would contribute to vibration in park. Any help would be appreciated!

awg

have looked at the tacho on bluetooth, and 50rpm variation sounds high..more like 10

I would say my idle variation is barely detectable audibly, (unless the A/C compressor kick in)

No vibrations

Morat

Have a good wiggle of your plug wires, you could have a poor contact or a short causing an intermittent misfire. It's a simple thing to eliminate before things get spendy.

ecksjay00

It was having the same issues before I replaced the coil rail with a brand new one from NAPA. Connection seemed to be good. I will poke around and see if that's the problem, but I imagine it would be difficult to peg it to one cylinder since I won't be able to check individual plugs and it's not throwing codes.

ecksjay00

I also will add, and I'm not sure if this is all in my head or very relevant, that it seems to idle smoother when parked/stopped on an incline (nose up) as opposed to nose down. It almost seems to idle slightly higher and smoother on the incline as opposed to the other way around. It's not particularly hilly where I live, but I notice it when I'm, say, halfway up an exit ramp. Not sure what could account for this, but any thoughts are appreciated.

Spencer_P

I have the same or similar issue on my 96. I don't have a tach but the one time it was hooked to a bluetooth scanner I know the rpm was changing just not sure how much. When in park and my door is open or my hand is on the steering wheel you can clearly see vibration.