Filler hose leak
 

The Porsche dealer wants to do an air leak test due to CEL I get occasionally at or near redline. The Fault is misfire cylinder 1 and 4. I changed the oil the other day and found I have a leak somewhere in the filler hose. Knowing that the there is a vacum on the oil cap when the car is running that has something to do with the AOS, could this be the leak they are looking for?

If it's the AOS, it will be very hard or nearly impossible to remove the oil cap while the engine is running. Do you have any blue smoke coming out of the exhaust. When I replaced mine I had just a very light smoke, hardly noticeable. I could not remove the oil filler cap while engine was running. When I replaced it, the boot on the bottom of the AOS was dramatically pinched in and could have been causing my problem. The AOS comes complete and runs around $120.00. Any vacuum leak will cause problems with engines running performance. They are the hardest to find. :cheers:

Have you checked the dipstick tube? I've seen several posts about people breaking theirs...

No smoke no broken dipstick. The AOS is fine and the oil cap does have a vacum when trying to remove the cap. What I am trying to hunt down is a CEL giving me a misfire code at very high RPM. I have been told its a possible air leak.
When I changed the oil the filler neck on the inside of the engine was wet with new oil and dripping. I wipped it off and no problem since. However, in order to leak, it must be cracked or pulled loose which from what I have read can happen.

And Yes, my plugs have been changed and coil packs swapped. They are snapped in place and not loose.

OK, I assume you have a mild vacuum at the oil filler cap and it came be removed while the engine is running fairly easily. If not, you may have a vacuum leak still in the line. The top J-tube has o-ring seals at both ends and the bottom tube also has seals at both ends. The tubes them self can crack since they are plastic. What year is you Boxster and how many miles on it.

The oil cap can be removed but I can feel the vacum when the engine is running. I dont know how much vacum because I have never compared it to another boxster but its definitely tougher when the engine is on.

97 with 33,000 miles