What is the difference between the 528i and the 528?

no difference. Theres no such thing as a 528 with out the i, unless u mean REAL old skool BMW 528, when they werent fuel injected. THats what the I stands for, fuel injected.

Hoiw about the 528i and the 528ia

Hoiw about the 528i and the 528ia

The only thing is, dealer's use the "ia" on cars to indicate that the car has automatic transmission, nothing more. when they indicate the transmission on the series numbers, like on records or documents, they either put for example: 528i for manual or automatic transmission(more likely manual because they always indicate the auto tranmission by using "ia"); and 528ia for automatic transmission. It also can be 740ia or just 740i.