I wanted to update this thread with where I am so far on this. After this was posted, I checked the purge valve with a vacuum test, which it passed.
I took the car to a local shop where the owner and lead mechanic is a former 20 year Toyota master technician. he also did a smoke test and could not see the leak. He also checked the purge valve. He admitted his scan tool was not as capable as Techstream, but he believes he identified the issue to be within the evap canister. So I replaced the evap canister. No change, the lights came back.
Then I took the car to Allen Toyota where the tech validated everything I had done so far was per the TIS trouble shooting process, and noticed that the gas cap has some condensation on it, which to him meant that the leak was at the fill neck. He tried a new gas cap, no change. So his diagnosis was that the fill neck needed to be replaced. To test this theory, I ran the car for an entire tank full of gas with a rubber glove under the gas cap so that the glove was like a seal. No lights. Progress.
So I replace the fill neck. Now to do this, you need to remove the evap canister. There are two connections on the evap canister, one to the top of the fuel tank and one to the PCV valve. The PCV valve one has this rather weird fitting.
Fill neck goes in, lights come back on. Now I'm perplexed. Did I mess up a fitting somewhere? The vacuum pressures generated in the test are quite low. like between -1 and -5 kPa. That is less than 1 psi. I'm aware that the hoses in the car are mostly 16 years old, so maybe there is an old hose barely leaking somewhere. So I buy a tube of Dupont High Vacuum silicone grease and grease up all the hose barbs, O-rings, etc. for the hoses I have removed. No change, lights come back on.
At this point I am getting desperate. The car is driven by my 16 year old daughter, and a rear wheel drive short wheelbase car designed to have a functioning traction control system driven by an inexperienced driver spells trouble. She complained of the rear end breaking loose a few times, sometimes in traffic. So if this doesn't get fixed, the car is getting sold.
I try taping the little plenum that feeds the PCV valve, thinking there could be a leak where the plenum is split in half. No change.
I keep coming back to the fact that the problem was solved with the glove test before I replaced the fill neck. So it had to be something related to that. I had removed a bunch of hoses to get that in. The Evap canister PCV valve connection came back to me. Could that be leaking? Problem is, that line goes all the way to the engine bay. Replacing that entire line would be a major effort. Fuel tank would need to come down, all the heat shields, etc.
So I cut a bicycle inner tube into a 6 inch section and slipped it over the connection. Then I put 4 or so zip ties on each side to cinch it down super tight. Its been about 6 or so key cycles and no lights. Fingers crossed, knocking on wood, etc.
