Post #30
Boxster hard to start after filling with gas - Page 2 - 986 Series (Boxster, Boxster S) - RennTech.org Community
"SOLVED!
This was a bear of a problem.
The whistle was caused by too much vacuum in the lines -- if you tapped the valve housing (#8 in previous pdf picture)
just right -- you could get it to resonate and whistle.
There were times it did not resonate at all -- at these times the vacuum was not as strong.
The key was determining this relationship.
There is a valve that controls the Evaporative shut-off valve. It was malfunctioning.
This valve is located under the intake plenum back in the engine. However the noise
emanates from the fuel door! Disconnecting the connector mimics the failure mode,
so in a sense the valve failed stuck open.
We pulled the hose that comes from this valve to the intake manifold right at the Y of the
hose that comes from the AOS. If we taped that hose off -- the engine ran fine.
If we left it open -- it mimiced the hard start after fueling to a T -- including having
to give it gas to keep it from stalling.
Once we replaced the evaporator shut off valve the vacuum reduced and was consistent.
The engine ran really well, and we have since filled it with gas with no issues.
Sadly I replaced the purge valve, and the charcoal canister up front to the tune
of $200 -- and a ton of wasted time. But now we know."
Also
http://rennlist.com/forums/996-forum/575816-questioning-the-reliability-of-the-996-starting-problems-fuel-vent-system-pics-12.html
post 167 for answer (Evap rejuvenation valve replacement)
post 101 on shows pics tracing the whole system on a 996.