Rough idle, loss of power. Options

[Chreeis]

Long story short, my 5s has a pretty rough idle when not in park. Got the car with no grommet in the pcv valve. After replacing the pcv valve and grommet, the car had a significant loss of power, and the idle was rough and low. So low that it would bounce around and eventually stall if I came to a full stop for too long. Reinstalling the original PCV/grommetless setup didnt help, so the car was towed to the mechanic, where they managed to get it to drive a little better, but couldnt solve the problem entirely. Ran some seafoam through it, and I got a lot more power out of the car, but the car would still idle rough and eventually stall(although it was significantly better than previously.) Last thing that I did was adjust the idle speed screw, and that seems to have acted as a bandaid for this problem, but I've read that this solution may not be permanent. No stalls since this, but the idle still gets rough. Heres a little list of whats going on.

The Bad
-CEL, showing p300-304(random/all misfire), P171(System too lean)
-Idle bounces ~700-400 RPM
-Loss of power
-When battery is disconnected, ECU seems to have a steep learning curve if you will, as it takes several days of driving before the car starts to drive somewhat normally again. Could be due to the lean fuel/air
-While at the mechanic, we ran some fog through the intake and saw that the EGR was leaking pretty bad.

The Good-ish
-Compression tests done at shop, cylinders okay.
-Seems to idle better when cold.
-The rough idle can be "fixed" about 70% of the time by turning on the AC. This makes me think the problem is air/vacuum related, and not fuel related.
-The rough idle also tends to go away once I get the car on the highway, or if I get it around the 4-5k rpm mark. Like the AC, this doesnt always work.

At this point I have ordered a new EGR and vacuum modulator, and am waiting on their arrival. If that doesnt solve the problem, I was thinking about replacing the injectors and fuel pump, as the seafoam did seem to help a little and the ones in my car are older and could use replacement anyway. Besides that I'm not sure how to tackle this issue. Any help would be appreciated.

[RocketScott]

Oil can leak into the distributor too.