Well, you could cut the brake lines, but that won't stop the engine, just the brakes. Or you could cut part-way through one of the belts (timing belt?), so that it would work at first, but snap apart at some later point.
Once, the car I was driving died because the garage had gotten water into the distributor cap -- the car worked fine at first, but later that night it stranded me.
And don't forget the lovely, all-purpose, vivid yet vague phrase "tampered with"
PJ
