Auxiliary belt tensioner
 

Just wondering if someone has had the same issue...just changed the aux belt and tensioner and all fine but the new tensioner seems to have a noticable vibration back and forth on the spring mechanism - is this normal? All other pulleys running true so seems odd that this should be happening umless the roller is sticking but seemed ok when i put in on although wasn't spinning completely free. Any advice gratefully received. Xc90 2008, 84k miles.

A failing clutch mechanism in the alternator pulley can cause vibration in the auxiliary tensioner so check that first.

Probably ok, usual cause is alternator pulley, however mine (v70 D5 163 e3) still hops intermittently after replacing alternator pulley...

Thanks - yes I did check the alternater clutch and seemed to be working ok and turning very smoothly.

The pulley should slip when you flick the pulley in the reverse direction , and drive the alternator when you flick it the other way .. try it with the belt off .

Ok thanks will try check again, or could be the power steering pump? I didn't look at that.

Highly unlikely to be the PS pump ..