I just finished installing a new engine on my 01 XJ. Everything seems fine but I have a pulsing like vibration that is not constant but happens every couple seconds and dosent go away until I start to actually drive. The RPMs are right around 5-600 at idle and they don’t really move when I feel the pulsing. The only thing I can notice is my harmonic balancer seems to have a small amount of wobble to it. Not up or down or side to side but just a wobble, could that cause my pulsing idle situation? If not I’m not really sure what else to check. Brand new Napa harmonic balancer was installed on this engine.

 

If the balancer is wobbling, it's probably seperating and needs to be replaced. Got a picture of it?

 

I have never noticed, or heard of anyone noticing a faulty harmonic balancer until it is too late..so I do not think that will be your problem, as described...but it could be

As having said that, harmonic balancer runout is unacceptable, so it needs to be replaced

I noticed mine by looking down the front of engine, and I could see that it had runout with the motor spinning

 

Hi,

was just reading in this forum for a while with no membership but just joined to be able to answer here.

I had the exact same problem. Pulsing vibration from time to time only in idle. Installed new harmonic balancer, timing chain. Did not help.

You already installed a new balancer and it seems for you that there still is a slight wobble. Please keep in mind that with these old vehicles you engine mounts can also be worn which can cause the whole engine to slightly vibrate. So when you concentrate on the balancer when you lay under the vehicle with the engine running it might seem that the balancer is wobbling, but in fact the balancer is fine and the whole engine just slightly moves.

Before buying a new balancer check you distributor. I had a slight left to right play in the distributor shaft. The contacts of the rotor and the distributor cap had some strange weld-like debris on it which indicates that there was direct contact. Its okay for the distributor shaft to have a little up and down play but not sideways. I replaced the distributor and the problem was gone. There is a chance that its the same with your engine.

This video is quite useful in my opinion:

When you replace the distributor, do not forget to get a new seal for the distributor to engine block surface and also put a new cap and rotor on it.

Hope that helps.