Revealing mistake: Towards the end of the film where Rambo shoots up the computers in a building and the spent rounds are falling to the ground. It is clear to see that these are blank rounds. Where the bullet would sit in the case normally you can see the case is extended, This is where on a blank it is just crimped closed due to the lack of a bullet.
Audio problem: In the shot early on, where Teasel jumps his car and breaks a fence post, his car horn beeps when the car lands on the ground. A few shots later, when his car falls down, then flips over on the embankment, the car horn gets stuck. It's a totally different car horn sound this time.
Plot hole: The national guard leader says a dozer wouldn't be able to get to that area where the mine was blown up which supposedly was around 500 yards from where Trautman and Teasle were dropped off in the helicopter. But in the following scenes Rambo crawls through the mine which is nowhere near 500 yards long and when he comes out of the shaft he's right next to the road filled with trucks and other vehicles. So why can't a dozer get there?
Continuity mistake: During the motorcycle chase, just after the police car breaks through the wooden gate, in the close up of Rambo's motorbike its wheels go through two puddles, a short space of land, then another puddle. Keep watching closely as he rides through the mud. In the overhead shot of Rambo approaching the road at an intersection, he goes through the same three puddles again (the third one is hidden behind a tree, but you can still see the splash).