Having a multisymptom problem that I'm stuck on .

Washed engine bay and water got where it wasn't supposed to. I removed TB and cleaned out all plug sockets and replaced plugs.

Idle misfires at low RPM and after driving a few miles I'm getting all the O2 sensor codes in the title. When accelerating moderate or hard it appears to drive normal (acceleration is great)

Well, I checked all the O2 sensors and Bank 1 Sensor 1 / Bank 2 Sensor 1 are within resistance spec of ~16 ohms and 12v is coming out of the ECU side to the plugs so it's not actually either O2 sensor.

Along with this, the idle will not return to low unless I rev the engine and enough momentum causes the engine speed to fall rapidly. I'm also hearing a high pitched sound from the area near the TPS. Upon further inspection the throttle valve vacuum diaphragm / valve does not seem to be working correctly but I have no references to this specific part in the factory repair manual. The more aggravating part is that the TB was swapped with an unknown 2JZGE years ago so it is not the original 1997 TB and I'm not sure what part is accurate.

What is this part and what can be done to inspect / replace it? It's the part with the black cover and the little piston valve is making the car idle very high or normal.

 

OK. Another long day of diagnosing stuff. It wasn't the throttle vacuum valve in the above picture.

I think the issue is resolved now. For anyone who stumbles upon this in the future - the error codes for something might not always be caused by that specific part failing. For example the O2 sensor codes I was getting were from a problem with the A/F because of the TB/TPS -not the actual sensor.

Long story - I had to adjust the throttle closed dashpot screw because it was preventing the butterfly valve from resting on the actual stop which is not really visible in this picture - just barely. It's not the red marked area, that's the decel dashpot. Like I said in the OP, this car came from some other model and I have no idea which so it was set differently. I backed off the screw then did a very slow and meticulous recalibration of the TPS (the factory manual skips the part on the 2nd duplicate set of instructions to check the TPS where you are supposed to apply vacuum to the throttle line before using the feeler gauges and do the IDL1-E2 tests.)

The issue of the car idle not returning to normal when the gas pedal was released is gone (so far so good). This has been going on for years and I never bothered to really deep dive until I had these issues. I've basically become accustomed to double tapping the gas pedal every time I stop to get it to go down. When you release the throttle now the idle slowly drops and returns to normal instead of sticking at 1700 or 1200rpm.

I also lubricated the throttle linkage along with the dashpot valve as I mentioned. Reapplied gasket sealer and tightened everything back up.

dashpot screw was set too tight and was preventing the actual stop from resting when vacuum was applied.