Fonzie shows his master mechanic skills for the first time.
When Marion tells Richie and Potsie that Trudy and Betty are meeting them at Arnold's, you can hear the voice over as Marion originally said Arthur's. The restaurants name was changed after Season 1, Episode 1 "All the Way," from Arthur's to Arnold's.
When Mr. Cunningham pulls into Arnold's looking for Richie, he parks right next to the '29 Ford hot rod which is universally known as Ralph Malph's car. However, there are other people in the car and Ralph (who was seen earlier driving a red convertible) is in Arnold's, the car not having been established as Ralph's quite yet. The car will be Ralph's from the fourth episode on ("Guess Who's Coming to Visit").
The boys purchase a 1950 Chevrolet Styleline De Luxe Convertible. It was not considered a lemon when new and its not old enough to be a clunker in the shows setting.
The title is a euphemism for a defective car whose problems not readily apparent before its purchase and can be applied to other products which exhibit similar characteristics.