So, the computer is throwing code P1416 and everything points to the air check valve on the pass side. I found it (go me!), removed it, and condensation (which smelled mildly like gas) spilled out of the valve. There was some dirty buildup which I knocked clean.

I can pass air through both ends. One is decidedly more difficult to blow thru than the other, but nevertheless, it lets air thru BOTH sides. It's only supposed to let air through one side, right? What would cause this?

Second, why would this intermittently throw an error code if the valve lets air through both sides all the time? Wouldn't the SES light come on and stay on? I've reset the PCM and it will come on after 20-30 miles of driving. Help!

 

Here's a few lines from my helms on P1416:

"A check valve that flows in both directions causes heat damage to the AIR system components."

PCM turns off the MIL after 3 consecutive ignition cycles the diag runs and does not fail. At last test failed, or current DTC, clears when diag runs and does not fail. A history DTC clears after 40 consecutive warm up cycles with no failures. MIL illuminates at second consecutive cycle diag runs and fails.

Sounds like you need to replace it with a new one.