Could be most anything, probably an emission canister or possibly the oil cooler return.

I have a buddy who was having problems with his battery not charging. The guy at NAPA told him to pull off the alternator and bring it in to be tested. This guy spent most of the day getting his truck up in the air and pulling the alternator. He took it to the NAPA store and laid it on the counter. The NAPA guy said "I thought you had a charging problem?" My buddy said "I do". Counter guy says "why did you bring me the starter?"

True story. A lot of people just don't know their way around an engine compartment.