Continuity mistake: The stolen Dodge is a 1974 model. Peggy tells Kelly that she was conceived in it. However, the episode "Christmas" (Season 7, Episode 12) has a flashback to Christmas 1974, showing both Kelly and Bud. Kelly's height had been marked on a door since 1972.
Rock of Ages - S7-E9
Continuity mistake: In this episode, Al has taken on the persona of Axel Bundy, a rock star, so he can fly first class with older rock stars. But before they start a jam in the first class lounge pre-flight, one of them calls him AL when he's prodding Al to join the group when all they knew him by was the name Axel.
Frat Chance - S7-E6
Continuity mistake: When Bud is talking about this being the year he will get a real girl, he drinks from the carton of milk and spills some on his shirt. Next time they show him the spot on his shirt is dry. The next it's wet again, and it goes back and forth for the entire scene.
Continuity mistake: After Kelly breaks the TV screen, each time the camera changes, the broken screen looks different each time.
Answer: It was one of the hoses connected to the engine, nothing specific, but to indicate that Al tampered with the vehicle.