ok makes sense I'll check into that thanks

engine will turn over fine but not start occasionally when the engine is warm. new plugs, gas filter. has been doing this for over a year. does not do this during the winter in the colder northeast climate.

when this occurs the vehicle will always start after several attempts. I have tried ...

well it ended up to be a bad serpentine coupler pulley under the air conditioner. the bearing was rattling.

great repair by the local volvo dealer.

on another site it was mentioned the decoupler pulley on the belt (serpentine) side is bad if you cannot rotate the air compressor pulley in one direction when the engine is not running.

would someone who has a pre 2011 xc90 3.2 try that and report back if your ac pulley free wheels when spun ...

found on other sites there are two decoupler pulleys - one on the alternator and the other on the serpentine belt side that can make the noise I am hearing.

not sure how to determine which one is failing.

I see on other forms the two decoupler pulleys can make this noise. one on the alternator and the other on the lower serpentine at thge rear end assembly drive (READ).

from what is posted on various sites, sounds like this noise may be a faulty alternator decoupler pulley. appears the alternator must free wheel in the unloaded direction. the noise is coming from the coupler block area.

well replaced the tensioner and idler pulley, and the engine noise returned. the stéthoscope does not reveal noise from the water pump or power steering.

stumped at the moment...

removed the belt tensioner, started the engine with no load on the coupler drive except the alternator and the noise is now gone. the tensioner bearing is not terrible by the spin test.

I saw abscape suggested isolating the tensioner on another forum. Thank you!

napa has the tensioner, pulley and ...

I've narrowed it down to bad serpentine belt tensioner bearing or noise from the coupler that drives the alternator housing. used a stéthoscope to determine this.

as suggested will remove the serpentine belt to isolate the belt tensioner.