2003 Subaru with 170,000 miles on it. Don't drive it much these days, just on weekends. Was running great until about a week ago, now the idle, when warm, surges a bit, maybe 100 rpm and the vacuum would jump from 18 inHG to 14 inHG, back and forth. At first the car still drove normally. Now I can only hit 7-8 PSI of boost. There is a hesitation when it revs off idle too it seems.

My guess was a vacuum leak (I think 20 in hg is normal), but i can't find anything, none of the lines look bad. I know i have the 'pill' installed. I did have an aftermarket BPV installed but replaced it with the stock one, no help. I reset the ECU but no help. Also cleaned the MAF, might have helped the issue a bit, but still getting lower than normal boost and a surging idle, but both possibly are better than before

There does seem to be a noise coming from the intake/TMIC area, possibly a leak, but the hoses are in decent enough shape

Idle Air Control Valve maybe? Just drive it more now that i cleaned the MAF?

Thanks!

Edit: Thought car info was in my profile, 2003 WRX, TBE, Catless UP, TXS UTEC w/ Pro tune and Streetlite flywheel