2006 EXT 4.2L I6
Just had the transmission swapped for unrelated issues, but there has been a squealing noise that happens when cold idle or the throttle is >~35% when warm, increasing with RPM for a few weeks before. Both the mechanic who replaced the transmission and the mechs at the office swear it sounds like a vacuum leak, and both have been unable to locate it. The mechanic who did the tranny swears it's coming from around the rear of the resonator, but the office mechs and I believe we've narrowed it down to the area just behind the power steering pump. There's no secondary air injection on this one, so that's capped, but I guess the gasket *could* be bad. We've disconnected everything up to the throttle body and still get the squeal. We've isolated the vacuum ports off both the throttle body and the vacuum port for the rear heat/ac unit, also to no avail.
According to the mechanic who did the transmission, there were also codes P0014, P0171, P0300 & P0306. I have only been able to replicate P0306 currently, but I've only done about 25 miles on it so far. I plan to check plugs and coilpacks tomorrow, but I don't think the noise or engine bog is related to that as it only happened once during the 25 miles and hasn't come back again, whereas the noise and bogging are pretty much consistent and the ST TRIM is reading between 0 and +5-ish with around 30kPa/9inHg on the MAF.
From everything I've read so far, everything except P0300 & P0306 seem to be stemming from a vacuum leak somewhere, according to those more mechanically inclined than myself. We've sprayed combustible around anywhere we can think of, including the valve cover. The only thing we haven't done is pull the cover off the secondary air port as I'm having trouble finding the gasket available nearby and I don't want to wreck a potentially good gasket without a replacement in hand.
Anyone got any other ideas of where to check for vacuum leaks?!