“Mystery Date” (1991)?
https://www.imdb.com/title/tt0102500/
Quote from the IMDb synopsis:
“His elder brother helps him with a car and a credit card to be successful. This simple story gets complicated because of the corpse in the trunk.”
If you think that this is the movie you are looking for, then please select my answer as Best Answer by clicking on the “Select” button.
wositcalled Selected answer as best
well done Casspir.