Plot hole: At the end of the film Mardukas reveals that he has been wearing a body belt packed with cash - "in the neighbourhood of three hundred thousand dollars" - ever since Jack detained him in New York. Are we to assume that Jack Walsh, an experienced, hard-bitten ex-police officer, now a bounty hunter who routinely chases down violent and armed bail absconders who would kill him without a second thought, didn't even perform a perfunctory search of Mardukas when he detained him? This man used to work for the Mafia! What if he was carrying a weapon? A body belt with three hundred one thousand dollar bills in it would be uncovered by even the most casual pat down.
Suggested correction: He was using $1000 bills. That's 300 bills in the belt which spread evenly absolutely could have been missed near his waist as part of his clothing.
Rubbish. I specified $1,000 bills as that would be the smallest package he could have secreted about his person, and it would still be instantly detectable. If he used $100 bills the package would be ten times larger, and he would have to carry a rucksack under his shirt.
Continuity mistake: When Jack Walsh is in the diner after losing the Duke to Marvyn he can't light his cigarette with his lighter the man behind the counter gives him a pack of matches and say "keep them", but when Jack brings the Duke to LA airport he comes down the escalator and lights up a cigarette with his own lighter.
Suggested correction: The lighter simply didn't ignite for him in the restaurant, and it did later in the airport. Lighters can be finicky like that, especially when they start getting a little low on fluid. Plus, smokers often carry 2 lighters.
Stupidity: Jack has been using Mosley's badge and identification to pass himself off as FBI. He never once uses this trick to commandeer a civilian car for him and John when it would have been the safest way to get to L.A. much sooner.
Suggested correction: Probably because If he did that, the car's owner like Red the bar owner would eventually call the FBI office to get their car back and then the feds would know the make, model, license plate, and the last location of Walsh and the Duke. The police would have caught them in minutes. Walsh had to keep a low profile.