Idling roughly, has a serging quality to it and the tac is going between 5x and 8x continuously.

Jeff, your answers should be down here. Doesn't the Throttle Body have a 'Learn Procedure', if replaced?

I would check the throttle body, where the fuel mixes with the air also clean all pipes/connections etc after that you should know where to go next, but give the "plate" inside where fuel and air mixes, carb

indicates a dirty injector
cheap try is a couple of cans of quality injector cleaner and have the fault codes read by an accredited service center

P1518 CHEVROLET Description The Throttle Actuator Control (TAC) module contains data which is essential for proper TAC operation. The TAC module continuously test the integrity of this data. When the TAC module is unable to write or read data to and from random access memory (RAM), or the TAC module is unable to correctly read data from the flash memory or and internal TAC module processor fault is detected and the Detected Trouble Code (DTC) is set.
Read more: http://engine-codes.com/p1518_chevrolet.html#ixzz21VOQMCZz

use a couple of quality injector cleaner in the tank
run fault codes
remove and clean injectors
check fuel pressure

First I would try running a bottle of good fuel system cleaner through it w/good quality fuel. STP or Gumout are 2 good ones you can get at any good parts store. With temperature fluctuations and quality of fuel these days it could very well be moisture (water) in your fuel causing symptoms. Audis, BMWs, VWs and Benzs are sensitive to bad /cheap fuel.

Try cleaning TAC valve, spray throttle body cleaner in upper right of opening clean well.

Have the idle air control valve and the throttle position sensor checked.

is it a V-6 or 4cyl. take it to autozone and have them retrieve the code...I have worked on all models of camrys...many problems can cause this like IAC valve(common on 4cyl) or timing is offset(very common on V-6). Transmission will not cause rough idle. Tacs on these models usually malfunction stemming from distributor cap/coil oil inside or just the tac itself. Hopefully this helps!!

First thing I would do is clean the throttle body if nothing changes check your mass air sensor if still nothing. change (or clean) your oxygen sensors can normally be found on the exhaust manifolds. also it couldn't hurt to give it an oil change and use a fuel additive to get rid off all the nasty build up in the engine I use BG 44K

That's all the information I have good luck!