Idle mixture????

Paul Tomblin wrote:
Our club's PA32R-300 has an IO-540 with lots and lots of hours on it.
After 20+ years, at this year's annual the compression was down a few
pounds on a couple of the cylinders, and the mechanic said he really has
his doubts about it passing next year's annual. That might be
significant, or it might not.

Twice this year, while people have been flight training in it (I was doing
a BFR this spring, another pilot was checking out in the plane for the
first time a few weeks ago), the engine has been running fine and on
rollout afterwards the engine died and couldn't be restarting. Both times
it was after doing some air-work (stalls, steep turns, etc) and then a
couple of touch and goes. Nobody has had any problems in a normal point
to point flight, although we've had the normal problems with hot starting
that's endemic to fuel injected aviation engines.

The last time it happened, the engine died at the airport where our
mechanic is based, and he pulled the plugs and said they weren't fouled
and they were dry (so the problem restarting wasn't that he flooded it).
Based on a suggestion here, I had them check the fuel pressure, and it
seems fine. Could it be vapour lock? Any other suggestions?