There are some BMW 318i in the fleet. They only have a 3-cylinder engine. They probably come with a Manuel transmisson. Afaik its the only car with a 3-cylinder Engine as Mercedes, Audi and Jag don‘t have something like that. So if they want to give you a 318i just ask for something different. Espacially at the airport you should be able to choose from different cars.
To be safe just book PWAR or LWAR. It‘s 5series / E- class wagons.