You Better Shop Around (1) - S5-E21
Continuity mistake: When the store employee comes over to ask Al and Peg what they were doing, Peg throws a bag of chips in the shopping cart and says shopping. When Al asks Peg what the ingredients are, next shot the bag of chips are on Peg's lap.
Answer: It was one of the hoses connected to the engine, nothing specific, but to indicate that Al tampered with the vehicle.