Factual error: When Marty travels back to 1885 and meets the Native Americans, we see a view from inside the car with the digital speedometer. The car is still going over 70 when the Indians are less than 2 metres away from the front of the car. There is no way the car would be able to stop that quickly from that speed.
Continuity mistake: When Marty is about to race against needles, the camera zooms in towards his car. Notice a big rectangular black object reflected on the car. From opposite angles it disappears and there's just green fields. The black object was most surely a structure to hide the camera equipment.