Factual error: The soviet military equipment isn't all that Soviet ... e.g. the helicopter is supposed to be a "Mil-Mi 24 Hind" (Pilot and system operator sitting behind each other), in fact it's just a French "aerospatiale puma" with additional mock turrets and so on (crew sits side by side).
Factual error: When Rambo is going through the Soviet minefield, he probes a couple of times very hard with his knife, and then he lunges forward. Now, jabbing hard into the ground where you think there might be an explosive device is as bad an idea as it sounds. Also, Rambo doesn't probe to the sides where his elbows and knees are going to support his weight. Also, he lunges forward farther than he had probed. And finally, the mine he does find is very big for an antipersonnel mine. It looks big enough to be an antitank mine.