96 Corolla Idle Problem - Please help!

Hello! This is a lengthy issue, and I really appreciate anybody who can help me out.

I purchased a 1996 Toyota Corolla DX (1.8) a few months back for a good deal. Only had 92k miles. It didn't have any issues really, but since then the idle has gotten really bad. I tried cleaning the throttle body, but I think that only made it worse. The mechanic I go to said my throttle body is bad, and I need a new one, but they don't sell them anymore! They tested and fixed any air leaks; none present. I know it could be the Intake Air Control Valve or Throttle Position Sensor, but the shop claimed I couldn't do just the IACV without breaking the body. I'm not sure how true this is, which is why I need some Corolla Veterans to help me out. My old manager suggested I may need to replace the EGR valve, but given the symptoms, I'm leaning towards the IACV or TPS.

Error Codes:
P0401 - Powertrain: Exhaust Gas Recirculation Flow Insufficient Detected
P0505 - Powertrain: Idle Control System

-High idle
-Not present on startup; gets bad after car warms up
-Turning on AC drops the idle
-Higher in park, lower in drive (1700 rpm / 1000 rpm)
-High enough in drive to let it coast and shifts into second gear, but then almost stalls
-Clicking noise heard every time I press the gas peddle, sounds like it's from the throttle valve
-Breaking with the idle issue is rough; feels like the throttle valve is staying open and applying opposite force to my breaking, causing shifting issues. Whereas with AC on, car is able to slow down normally without weird feelings(described below)
-When breaking, car shakes and feels like it's going to stall for a few seconds before it finally shifts into lower gear. Sometimes will be stuck in this rattling stage unless I break harder or apply acceleration.
-Super rough shifting from Park to Reverse/Drive when high idle present

My uncle is suggestions I test the conductivity of a new IACV and TPS and compare it to my current ones before purchasing and replacing. Does anybody have any suggestions for me? I really don't want this to wear down the transmission; this car could last a long while if I find a remedy to this issue!
Invest in a Haynes or Chilton’s manual, it will help with diagnostics, also with those faults it’s entirely possible that the EGR valve is fouled, I’m away from mine right now but I’ll double check my hypothesis when I get back