I'm going to buy a car. (intention 99% of the time) I'm going to buy a car at the XYZ dealership. (intention) I'm going to the XYZ dealership to buy a car. (movement) I'm leaving to buy a car at the XYZ dealership. (movement) I'm leaving to buy a car. (movement) I'm going to buy some milk. (intention 99% of the time) I'm leaving to buy some milk. (movement)

Theoretically, it could be either. Usually, it would be the first, but it could certainly be the second. You would need to use context to work out which one is true. e.g. You are at a party, and someone says "I have a job now, I'm going to buy a car", then it means 1. She is at a party, she is not going anywhere. If your see your friend on the train, and ask him "Where are you going? I don't see you on line 2 very often", and he replies "I'm going to buy a car", then he probably means 2.

If it's written/said as "gonna" this almost always denotes intention rather than movement. I've never heard someone use "gonna" for movement unless they were saying "I'm gonna GO buy a car." "Gonna" = I'm going to *do action* "Going to" = I'm going to *do action* or I'm going to *destination* For example, you would not hear someone say "I'm gonna supermarket," instead they would say "I'm going to the supermarket" or "I'm gonna go to the supermarket" (typically, even in this case the second is less concrete in whether it will happen or is happening due to the use of "gonna" rather than "going to"

First