Hello everyone, I have a stock 2000 XJ with a 2.5L, 5 spd trans.
The engine starts good and runs well, doesn't stall out, but there is some vibration at idle. When I put the AC on there is a lot more vibration.

• I've taken the belt off and checked the condition of each rotating part to see if there might be one that wouldn't be rotating freely and causing a drag on the engine. Everything seems to be in good shape in that regard.
• I was told from the previous owner that the AC is a fairly recent replacement. It may have a small leak because I had to add freon. It cools off very well.
• I've replaced the forward O2 sensor (the after sensor is yet to be changed since its being a little stubborn)
• I've replaced the spark plugs.

Some things that maybe be a problem, but looking forward to any input you folks might have, are possibly a vacuum leak, or maybe a motor mount.

What might be some other things that might contribute to this vibration?

Thanks in advance for any suggestions

Regards

 

a bad motor mount could cause a vibration at idle that could get worse when the load of the ac is added. Is it running at a steady RPM? If so and the mounts look iffy they’re fairly cheap and not too difficult to rule it out. If you haven’t done so already, cleaning your throttle body and IAC is good preventative maintenance for idle issues.

 

Poni is right.
It can ad more vibration to the 2.5L shaker motor.

The 2.5L is notorious for vibrating things loose on the Jeep Wranglers, and Cherokee's.
Make sure you have spark to ALL 4 cylinders, and also make sure that your injectors are working properly too.
If your down one cylinder, your gonna feel it for sure!

 

Factory recommendation is to replace cap, rotor, wires and plugs every 30,000 miles. You changed only plugs recently. Any idea how long it's been for the other parts?

I would check and make sure the intake manifold bolts are snug and clean the throttle body.

 

Thanks for that feed back. I'll take a look at those motor mounts.
I did remove the TB and cleaned it well. I forgot to put that on my list of 'have dones'.
I had also attempted to replace the IAC but the one I ordered, though it was very close, the connector wouldn't fit. I need to revisit that and see what I can do.

To replace the mounts, I'd have to jack up the engine enough to slide the old ones out, correct?

 

I'm not sure about the plug wires, cap and rotor. So that would probably be good to do anyway. Might as well.

Hadn't thought of the intake bolts being loose but I'd think that if they were loose this thing wouldn't run too well, right?

 

Try just giving the old IAC a good cleaning. For the mounts, change all 3 at the same time. Loosen the bolts, jack the engine up with using a block of wood under the crank pulley, swap them out. The rear (trans) mount support the trans and drop the crossmember to access. Plenty of write ups or YouTube videos with more details.

always good to have a fresh start with tune up items.
if the intake is loose (or you have other vacuum leaks) your rpm’s will be really high, it’s very noticeable. Try briefly unplugging a vacuum hose from the manifold hose and you’ll see 😂

 

Come to find out, the motor mounts and trans mount on this jeep are an uncommon variety. I've seen an old post where someone was chasing this same issue. I believe they found some motor mounts from an old grand cherokee were the same; or at least they looked the same. The thread sort of died so I don't know if they actually worked in the end. It seems at some point Chrysler was using different mounts here and there. I wish I had the common type.

 

Ummmmm OK?
But a very quick search on rockauto.com lead me to this.

https://www.rockauto.com/en/catalog/...tor+mount,5552

 

This type is available at many places but they're very different than what I have. I'll try and get a Pic of one of them if I can.
Unlike the triangular shape to the ones that are readily available, mine are round and I think they're about 3 1/2" in diameter.
If I knew there was a way to use the common type I'd switch out so I wouldn't have to mess with these. I'll have to research if the rubber inserts for the Grand Cherokee MM's can be squeezed into the steel sleeve that I have. Thats if the old ones will come out of the steel sleeve. You'd almost think that there would be tons of reference for these odd types. I would guess that there are plenty of XJ's with this type of MM as well. I believe I'll have the same issue for the Transmission mount.

 

Get pictures of yours.
I bet someone added aftermarket mounts if they don't look like any of these?
Are yours painted yellow by any chance?