[ike84]

Blue -

It is the same here I have never had any issue with my Boxster so there's that.
I have probably read all the same posts here on the forum relating to vacuum leaks and other performance problems as you have.
On other cars like early classic's (Jaguar, Austin Healey, MG)
and early American cars that are running Carburetors.
I have seen multiple instances of single bank vacuum leaks I have also seen single or multiple cylinder vacuum leaks on cars running multiple carbs.
Almost every time that it has been a single bank vacuum leak the leak has been at the gasket between the manifold and head. Or in an intake runner.
On Multiple Carb. engines like a Jaguar that is running three carbs I have seen vacuum leaks on two adjacent cylinders.
Each Carb. feeds two cylinders. Those leaks have always been at the Carb. to intake manifold gasket.
So I would say everytime I have seen this type of vacuum leak it has always been very very close to the intake valve.
Or isolated in some way such as a leak in an individual intake runner or base of a Carb. on a multi Carb. setup.

One thing I think I see here on the forum is someone gets a code that indicates a lean condition.
They think Unmetered air Vacuum leak!
They also have misfires.
Vacuum leaks cause misfires right!!!
So they think vacuum leak.
But misfires can also cause the O2 sensors to report a lean condition.
Which looks like a vacuum leak.
Positive fuel trims confirms it.
They cannot find the cause of the misfires so they think single bank vacuum leak.
Now you have a situation where you have identical symptoms for two different types of problems.
Fertile grounds for a misdiagnosis.
So I think there are times when a lean condition is reported on a single bank. That is thought to be a vacuum leak when the lean condition is caused by the misfires.

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