I think at this point you would have seen a PXXXX code for the evap (small leak, etc) - the evap monitor cycle is the toughest monitor to set.

 

In my experience, for a small leak, the evap syetm will eventually throw a code. There is a test procedure involving pressurizint the tank and measuring leak down, but the several places mentioned can all leak to an extent that will prevent a pass but will take some time to code.
I will tell you once more, then I will not tell you again. The gas cap is the most likely thing in the tank evap circuit to leak. Think about it.

 

Any code needs things to be definitely faulty enough to detect it, so you won't necessarily get a code.

(Gas cap is a possibility but nothing like the only one.)

 

"(Gas cap is a possibility but nothing like the only one.) "
You are absolutely right. But... See "Occam's Razor"

 

So... which make of PCM is it? Denso? If so, which one?

 

I bought a new gas cap, should come in the mail next week. Figured I'd give it a shot, what have I got to lose? (Besides the 30 bucks it cost me.)

I tried cleaning the seal around the gas cap for ***** and giggles to see if maybe some dirt was preventing a quality seal, and then reran the evap clearing test. No dice.

 

That cough suggests the ecu is trying to run the first evap leak test and there is a
problem (leak) that is upsetting the engine.

It then finishes trying to run the test and all is smooth again.

A full visual check would be useful in determining if there are disconnected hoses, etc.

 

So, I recently replaced the part load breather hose, any other leaky hoses you think would likely cause this to happen?

 

All of the hoses from fuel tank (except the fuel lines) are suspect. There are also some valves that are involved in the test sequence.

Some of the advice already given is not completely applicable to your car, since, like my wife's, it has the new 20 thousand leak detection. However, even though the procedures given were not specifically for your car, I believe you have some problem or it would have passed with what you have already done.

The correct evap readiness test procedure for your car, according to the JTIS manual is in the attached pdf and as a jpeg below.

You should probably make time to download the JTIS manuals (look in the Stickys) for the evap system hose routing. If the gas cap is not the culprit, you will likely have a little harder time finding the problem. You are looking for a tiny leak in either a hose or one of the valves. A smoke machine is a valuable commodity for this kind of diagnostic!

Good luck.

 

And, if you want an idea of what's involved if it ain't the cap, peruse the attached diagnostic procedure for the evap system. You really want the cap to fix it , I assure you!

 

Quite a few tools will do "mode 6" in case you have one. (But most won't.)

 

Alright, my new cap is on the way to me. I have a handful of things to try, it seems.

 

Good luck, and keep us updated! You ain't the first nor will you be the last with an evap readiness issue!

 

was in your exact spot last november with inspection overdue and all.......it sounds evap....despite the new part......mine was fixed with a new purge valve good luck....

 

So I replaced my gas cap. I drove a good distance, probably ~75 miles. Now my car just threw an error code, P0455, with the "check gas gap" error message. And FYI, I checked it, and it's on there fine.

One of the things I already checked was this, after driving for a bit I went up to the gas cap and smelled all around it... no smell of gas, so I don't think it's leaking there. Any other candidates?

 

Well, that seems odd, indeed. Old cap not throwing a code, and new one doing so. And a large leak code at that!
So, the probable causes:
Fuel cap off
Fuel cap seal defective
EVAP system leak (canister damage, pipework damage)
EVAPP valve to ECM drive circuit open circuit, short circuit, high resistance
EVAPP valve power supply circuit open circuit
EVAPP valve to engine purge pipe damaged / blocked / leaking
EVAPP valve operating vacuum hose leak / blockage
EVAPP valve failure
Fuel tank leak

If you know someone with a smoke machine, I expect it would be real helpful from here. And since you have been into the area of the engine around the TB, look for cracked hose fittings on the evap components on the firewall there. And, as plums suggested, a good visual check again. Then, I would say you need to go through the JTIS diagnostic procedures previouly posted, or throw parts at it and go for the purge valve as jagjunky suggested.

Good luck.