98 Grand Marquis engine component ID
 

http://imgur.com/vdEvr

I need to ID this part if you guys could help.

Its directly next to my coolant reservoir. The black cylinder I circled has condensation all over the top of it (after my roughly 40 minute drive home from work). Is it something that I should be worried about or normal? I just had my intake manifold replaced and then on Friday I had my #3 cylinder start to misfire. My mechanic pulled out the spark plugs and sprayed cleaner into the cylinder and onto the plug, blew it all clean w/ compressed air, and put the plug back in. He cleared the code and the misfire stopped, but I'm paranoid and I want to know if I should be worried.
Thanks for the assistance!