The car being angry as a Running Gag. Apparently according to Taylor the car is sentient and only works when it wants to. As seen in the finale of 2.
Steven: You can stay in the house, you can have my aura, my spirit, the ghosts, the whole deal. The WHOLE CASABA!!!!! But keep your hands off my car. Hands off!!! It's worse than it was before.
Taylor: The car's still angry huh?
Steven: Angry? That car is PISSED!!!