Ins and outs of an idler pulley

So on a '96 XJ 4.0 I believe the pulley you adjust for belt tension is called an idler pulley, but are any of the other pulleys called an 'idler pulley?'

Reason I'm asking is my adjustable idler pulley was wiggling in it's bracket so I ordered an 'idler pulley' off rockauto that was not labeled correctly. Apparently it was grooved, although not labeled as such. But, because it was labeled as 'idler pulley' I assumed it was the adjustable non-grooved pulley I needed to replace.

Basically if the adjustable pulley in the 4.0 is the only one called an 'idler pulley' I'll use that as leverage for them to refund my shipping it back to them.

At least on 97-01 there is only one idler pulley and its a smooth pulley.

Looking at Rock Auto, for Jeep Cherokees, they list both a smooth and a grooved for 1986-2001.

It looks like you didn't notice the dual listing, didn't know/check the vehicle, and purchased the wrong one.

Chalk it up as a learning lesson.

Apparently non a/c 4.0s have a grooved pulley where the compressor is. Gotta say in 11 years of taking care of this truck this is the first time the part didn't actually fit after drilling down through all the year, make, model, etc choices on a parts website.

The adjustable pulley is usually referred to as the "tensioner pulley". An idler pulley is usually a fixed position.

Although having just looked at Rock Auto's catalog, I can see how the mistake was made.

They just got lazy and called them ALL idler pulleys....

An Idler pulley is basically defined as a pulley that is there for belt routing purpose, it is a just a free spinning pulley. You can have multiple Idler pulleys on a engine. I don't know about the 96 but my 95 has one Idler pulley and my power steering pump is the tensioner. If it is used as a tensioner it is no longer a Idler pulley. Hope this helps.