So I installed a CAI on my 2008 3 about two weeks ago and since then I have had two instances where I have thrown a code for a misfire (both in cylinder #3).

I have changed the plugs and while doing so have also noticed that my valve cover gasket is leaking enough that the one of the plugs had some oil on it when I took it out (the cylinder closest to the cam drive).

Would either of these cause a misfire or is there something deeper in the works here?

Any help with this is greatly appreciated.

 

Mileage? Oil on plug in cylinder may cause misfire. Ever change PCV Valve?

 

80k on the clock and have never changed the PCV valve.

I have a new valve cover gasket on order and will replace when it's in.

 

Change your PCV valve. A faulty PCV valve can send oil into the intake and getting in to the cylinders.

 

After looking further into the situation I noticed all the oil leaking in on top of the valve cover. I have checked the oil cap and doesn't seem to be leaking there.

I ordered a new pcv valve and it doesn't seem to be the right thing as it was a 90 degree fitting as where the stock one is straight, but the stock on doesn't seem to be a valve at all but more of a pass through, is this correct?

Is there any issues with putting a filter on the valve cover instead of the line from my intake?

Any help with this is appreciated.

 

I did a search and came up with same 90 degree: 2008 Mazda 3 PCV Valve in Canada - Canada 2008 Mazda 3 PCV Valve
I am not familiar with the 4 cylinder at all.
Putting a filter on the valve cover would be smelly and you would have to plug line going to intake. Some people have installed an oil catch can in between as well. Line goes to catch can, then from can to intake. Once a month (I think) you empty it. This however usually promotes sludge.

Mazda 3 Oil Catch Tanks at Andys Auto Sport

For more info please search: oil catch can mazda 3