So it appears the idler pulley will not be an issue, they also still seem readily available for replacement and fairly inexpensive, so no worries there. Thanks

Regarding the air pump, I managed to look at it more closely and it seems that one of the blades is slightly touching the inner hub. Both the pulley bearing is fine as well as the main pump bears as far as I can tell. No play, and no roughness, just the fan blade touching the inner cylinder wall in one spot. This was far more noticeable spinning it counter clockwise rather than the normal clockwise rotation.

I shot in some PB Blaster oil and spun the pump counter clockwise until I could no longer hear nor feel any hangup. When turning the pump over to drain out, most of the fluid was black, as in carbon soaked.

I assume that the exhaust check valve had a minor leak, not noticeable enough to leave an obvious sign on the tubing or exhaust port of the pump as they were clean with the exception of some carbon dust when wiping with a white towel, otherwise visually looked good.

The intake filter, while a little dirty on the outside was very clean on the inside, as was the intake chamber. Either way it seems some crud had accumulated over time and was sticking to the blade tips, causing the scraping, screeching.

Since it tested on a bench only with a power drill spinning the pump, I cant confirm completely, I'll have to get it back on the car to see of the belt tension and or rpms tell a different tale.

If you have some slight noises from your air pump, it may be worth taking it off and inspecting and cleaning before you go off to replace it, or worse, let it slide until you are forced to replace or remove it. Worth a shot.

You could use carb or brake cleaner, but if you have PB Blaster or liquid wrench, you'll get similar cleaning results and get some lube in there anyway, low risk to the internal bearing.

__________________
Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)