Plot hole: Captain Smolsky only gets hit in the back with the plaster. So why, later on, is his entire body covered in hardened plaster, like a mummy?
Plot hole: In the runaway train scene, Gene Wilder uncouples the train from the forward car, and has to make a dramatic leap to get back to the uncoupled car. Is there any reason he couldn't have uncoupled the train from the back car and just stayed put? It seems an unnecessary bit of drama.
Plot hole: When the Ferrari stops for fuel at night, Franco decides to spend the night with the girl in the Mercedes. His partner protests, then abandons Franco to continue the race. The next morning, the girl drives Franco to meet up with the Ferrari again. This is a coast-to-coast race, planned out in detail by each crew long before to take the shortest course at the highest speeds possible. First car to L.A. wins. It isn't possible for the Mercedes to just 'catch up' to the Ferrari the next morning unless the Ferrari was taking a wildly wandering course or driving incredibly slow for hours.
Plot hole: Funn, Eggs, and Bell, accompanied by Vilma, enter the theater, ready to show their finished Silent Movie project to the audience. However, only a night previous, Funn, inebriated, is rescued from the gutter, by his friends. A scene immediately following, shows them 'reviving' him with coffee. When did they find ample time to shoot their film? The time frame doesn't add up.
Plot hole: Since the criminals who used the dogs to rob the bank in the first movie were never apprehended (No criminal worth their salt would tell the authorities their caper was spoiled because the canines ran off with their loot), there is no way the people who are hunting the dobermans in the beginning of this movie would know the dogs were still carrying the cash. (00:18:00)