Can I get away without Toyota parts for plugs, injectors, or coils?

Throttle body replacement is the only known repair method for Throttle body position sensor, because there's no way outside of the factory to calibrate if you just swapped the sensor.

Sounds to me like there's no new problems with your car, just same problem you had before with unstable idle and you'll likely find P1121 again. Just put in another used throttle body from the wrecker. It's just some plug, nuts, bolts, clips, very easy job....

 

... and of course, the correct cookie cutter text for a P1121 is Coolant Flow Control Valve Position Sensor Circuit Stuck.

There are plenty of posts in the Gen 2 forum about that, some of which will have the repair manual except for how to troubleshoot and repair this problem.

This code will be set if any of the following conditions are detected:

• Water valve position sensor output voltage:
  • No change despite the ECM sending a valve control signal or slow response
• CHS tank outlet temperature sensor output:
  • 60°C (140°F) or more (when hot coolant recovery starts)
• CHS tank outlet temperature sensor output:
  • No change despite the hot coolant being recovered

 

Oh heck, was this another of the "somebody googled a P1 (manufacturer defined) code and got the meaning it has in some other model of car" stories?

 

Sounds like The Three Stooges Garage...

 

A bad radiator cap can result in unexplained coolant loss. The OP might very well have the original cap, and at more than 300K miles, it may be on its way out. There are no drips when this happens, the coolant is lost when hot, and evaporates leaving no signs. Pressure test the cap to see if it is still good. Note, I recently replaced a cap on an Accord with one from Gates (usually reliable parts) purchased from RockAuto (reliable vendor). I happened to have a pressure tester on loan, and in an abundance of caution, tested it before installing it. It was bad - wouldn't open at any pressure. So got a refund from RockAuto (for obvious reasons, they didn't want the part back) and bought an OEM Accord cap at a local dealer. Tested it too (paranoid by this point), it was fine, and problem solved. We had thought this might have been a bad head gasket, but with the coolant loaded with dye and the cooling system pressurized there were no leaks into any of the cylinders, nor were there any external leaks, nor any contamination of the oil or AT fluid. At that point pretty much all that was left was a bad cap.

One thing about ordering multiple parts from RockAuto - they don't necessarily come from the same warehouse and the shipping times can vary dramatically. I have on occasion picked a different part (where it didn't make much difference, like for a cabin air filter) in order to get the parts faster. In cases of "needs to be Denso" then I just wait for the part.