What would be more appropriate? Jumping in the cold seat, I crank the ignition. or Jumping into the cold seat, I crank the ignition.
In the older, more malleable English. Incidentally, the reason that it is 'into' and not 'in' is because 'in' is a state-of-being verb, (He was in the house) whereas 'into' is a preposition (Where did he go? He went into the room.)