Continuity mistake: Al and Bud are being hunted because they are the final male Bundys. However, earlier, in Baby Makes Money (Season 4?) Al and Peg went to the funeral Of Al's uncle, Stymie. There were other male Bundys. The heirs had to produce a male heir and name him after Uncle Stymie to get all the inheritance. The 3 England Show episodes all have the premise that Al and Bud are the only male Bundys left.
Revealing mistake: While they are jousting, there is no one at all next to the stage in the wide shots. Every time they show the stage up close, there are 40-50 people. It changes back and forth the whole scene.
Continuity mistake: At the airport outside, Marcy yells at Jefferson and knees him. While she does that, there is a man wearing a white coat walking behind them. Camera instantly changes and there is no man at all in a white coat. In fact, there is now a woman wearing a white coat.
Answer: It was one of the hoses connected to the engine, nothing specific, but to indicate that Al tampered with the vehicle.