Replaced UIM on my 96 Bonneville SSE, car is running good but now there is a loud whining sound when the car is at or below 1500rpm, although not all the time, but frequently. As soon as I rev it past 1500rpm it stops. When slowing down, it comes back (right at 1500rpm!). This never happened once before we replaced the UIM. Doesn't seem to be coming from the accessory belt area and the AC/fan is off. Also noticing the oil pressure gauge getting lower as I idle (just below 40, not getting into red though) and then kicking back up closer to 40 when I accelerate. Oil levels look good.

Any ideas?

check for vacuum leaks did you install 2 0 rings on the egr one large orange and a small black one on the egr

I think you mean pcv
Well I hope you mean pcv cause I can't recall an oring on the egr.

oupss youre right popatim its pcv

That almost sounds like mine when we forgot to put the PCV valve in at all It screamed up until 3-4k rpms.

That would be the first place I would start is the PCV and connections associated with it.

The PCV valve should be located underneath your MAP sensor on what would be the left side of the manifold if you were standing in front of the car.

I think so anyway, Im just going off memory, and its been almost 2 years since I messed with a 3800.

You remember quite well. Thats exactly where it is.

Your PCV valve should have an o-ring at the top and bottom. I bet if you pull your oil cap at idle, you have suction, too. Am I right?

Thanks guys, we forgot the PCV valve entirely, problem solved.