As many others have discovered, the PCV valve diaphragm for the AES motor fails most likely due to the harsh environment and/or age of the component. New replacements are essentially non-existent and crazy expensive if you find one. A used component, if you can find one, may fail in short order again given the age/construction of the component.
In my case, the PCV valve failed in two ways. First, the vacuum line/side of the PCV was compromised allowing the suction of engine gases into the intake manifold causing a lean condition. The computer compensated by adding more fuel to correct the lean condition as measured by the front O2 sensor. Gas mileage had suffered for some time and I was unable to track down the cause as there was no check engine light nor was there a noticeable drivability issue. The partial load/long term fuel trim was running at 12.5% which is well above the specification of -5 to +5%. I replaced the original O2 sensors (140k miles) as their response were a bit sluggish and thought it may be contributing to the problem but there was no improvement in fuel trim. I then replaced most of the vacuum lines which were in fair shape but not terrible. In replacing the vacuum line to the PCV valve, I happened to check the PCV operation by sucking on the vac line to it and found the vac diaphragm had failed. I then plugged off the vac line and nipple to the valve. Bingo, fuel trims corrected and ended up in the range of 0-1% and the idle seems slightly smoother.?
A further check of the PCV valve found that engine side diaphragm was also free flowing engine gases to the intake tube/throttle body in vacuum/load conditions which likely messes with the fuel trim in load conditions. Since replacement PCV valves are hard to come by, following is my fix that might be of interest to others.
I wanted a dependable quality made part that was easily serviceable and/or replaceable along with no modifications to the original configuration should a quality OE style part become available (highly unlikely). I settled on Toyota part #12204-20040 which fits various 3.0-3.3L engines from 2001-2006. It's compact, designed to be mounted horizontally, and for an engine approximately the same size as the 2.8L VR6. Here's some pics of my MacGyver configuration.
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