+1

does the car still have a stock TB plenum or aftermarket?

Car has the IPD plenum.

I lowered motor and used soapy water. If anything is leaking it's not showing any bubbles.

At Sam's suggestion I pulled up a PET http://www.porsche.com/all/media/pdf...7T_KATALOG.pdf

And am looking to see what check valves there are. Any idea which one vents the oil tank? Or would be involved in the 'whooshing' sound I hear when I open the Oil Fill cap?

You will not see it in pet since on 997 the check valve is built into the plenum. IPD had an external check valve. You will also not see soapy water bubble since check valve leaks from plenum into the tank. Lower the motor and follow the larger line that goes from oil tank to check valve behind IPD. That valve is likely bad which is why you hear air coming with the oil cap off. Happy hunting...

Any idea how I test to see if it's bad. And if it is what should I order to replace it? Not sure of what part #.

I appreciate the help!!

well if u hear air going into your oil tank the checkvalve is bad ... pull it out and blow in it. it might be stuck or installed backwards. as far as replacement goes, contact IPD for a new one.