Was hoping to get some help on interpreting the results on my 2002 SC430...yea, I know this is an LS430 form buuut the EVAP systems are the same. And the LS430 is a much larger community. So, apologies for my refugee status...though, I do own an LS430 as well.

Having said that, here's my issue. I'm getting a P0440. So, I do the EVAP test on Techstream. This is the graph of the fuel tank pressure throughout the test. Here's what's confusing me. The rise in pressure duing the period where I have drawn in a green bar above is fast. This would indicate a leak. However, when the test is repeated under the exact same conditions during the orange bar, the leak is gone. I believe the term to describe this is hysteresis.

Has anyone ever encountered this and where the hell do I begin? Appreciate your insights.

 

It could be an actuator that gets stuck and after the first cycle is good but after a night of sitting doesn't cycle.
Smoke test is the best way to troubleshoot evap issues, can rent one or pick up one from amazon for 75-80.
Toss it on the evap line then run the test, where its leaking you'll see a ton of smoke.