× We were into the car when we heard the explosion.
√ We were in the car when we heard the explosion.
We use into only when there is movement: ‘I jumped into the car and started it’ ‘I put the exam into the drawer.’ ‘I went into the kitchen to make an omelette.’
We use in with or without movement. You can say both:
- ‘I went in the kitchen.’ (movement)
- ‘I was in the kitchen.’ (no movement)