Wife comes home and says the tire is low. I check it out and it's completely flat. I go to fill it up and after I do I realize that when I move the valve stem in all but one direction I get psssssst.

Is this something I can fix or do I need to take the tire to a shop.

FYI, this is a standard valve stem... aka no TPMS.

 

You need to take it to the shop and get a new valve stem.

 

Could just be the valve core has come loose a bit. You can buy a valve stem core tool to tighten it if it is indeed loose from your local auto store.

 

I had an ugly surprise last week - flat tire on interstate.

I have 17" webspoke wheels with the standard tire pressure monitors on my 2009 MCS Convertible. These metal inflation stems have a nut on the outside that holds and seals the tire stem to the wheel. The nut had come loose and there was nothing wrong with the tire. Once I had the correct socket it took almost 3 full turns to tighten the nut !!! This car has only 15,000 miles on it. The other three stem nuts were fine.