My XJ is around 4 inches in the rear and 3.5 in the front and the vibrations are only bad when in idle. They go away more at speed. I have new 3 inch pro comp leaf packs with built in leaf shims, i believe they are 4 degrees. I recently put in iron man poly motor mounts which definently give more vibes but i dont think it should be as bad as it is while stopped. When i have the jeep in Drive it vibes way more than if i put in in Neutral. Any ideas? i dont have a slip yoke eliminator.

 

Are we talking about engine vibes here? Or driveline? Bc at idle any vibration you feel is from the motor. Doesn't really matter what size lift, sye or not.

 

When was the last time your spark plugs were changed? That may make a difference.

 

Sounds like a real rough idle or a misfire to me. Any codes/CEL? Mine did that for a while. There's a TSB on it. Apparently, the exhaust valves get sticky and cause a miss. I ran a can of seafoam through it and it hasn't happened since.

 

Im actually not sure the last time the spark plugs were changed. It does throw the code saying cylinder 3 misfire like every other 2000+ XJ but it has turned off by itself the past week. It would be strictly engine vibes at idle in drive? it would have nothing to do with drive-line?

 

O2 sensors are picky on 00/01 xjs. If you replace them you really have to go with mopar even though they are exoensive..

 

Do you think 02 sensors could be causing such a bad vibe?

 

You replaced your motor mounts but how does your transmission mount look? Honestly that would be my first look.

 

Does it vibrate when the motor is cold? Or only when warm?

 

More when cold but it never really stops when warm. Some days are worse than others when warm with the vibes

 

Trans mount mine had a knock at idle off and on. I replaced all the mounts and its much nicer to drive. I will not put thane mounts in a DD ,I had thane in one car it was hidious.

 

My rough ride was mostly fixed by replacing the spark plugs. It still runs a little rough however.

 

Did you notice the vibes as soon as you replaced the mounts?
Poly will deff. vib more.

If not,it's not the mounts.

 

The poly mounts will attribute to that vibe big time.

And also, with the jeep idling in drive it's your engine that's causing a vib. Nothing in the driveline is spinning when your idling with the trans in D at a stop.

Did you change the trans mount also? (didn't see an answer to this one)

Assuming the jeep is running Ok, (tune up has been done recently along with TB and sensors cleaned out) I would say the poly mounts and the chance of a bad trans mount is your issue. Vibes will transfer from the engine to the trans and then to the trans mount. Make sure it is in good order. If you upgraded the engine mounts it's a good idea to upgrade the trans mount.

 

I noticed the vibes after new mounts. I upgraded to poly motor mounts and replaced my trans mount with a stock replacement. I will have to get a tune up with new spark plugs soon to clear that possibility. thank you for all your help guys