Not a car, but a Yamaha 500 single I bought in the Philippines some 12 years ago. It looked like a real nice bike when I bought it, but I soon discovered it was a total shed under the black paint and shiny engine cases.
It would not idle properly, 'just needs the air screw adjusting', the previous owner assured me. I finally discovered the spring on the air screw was the wrong one, 5mm too long, so you could never actually 'bottom the screw gently' and back out 1 1/2 turns. I then found the vacuum operated fuel pet cock had no innards, and you could not turn the fuel off.
The fuel tank cap was held together with wood screws.
The front forks had a 4mm groove in the steering stem, where the bearing cups were in upside down. It had basically sawed half way through the steering!
The drive sprockets looked brand new, but the chain was 100 years old. Why would they swap the sprockets out, but use a totally shot chain???
The alternator didn't charge, 'has a loose wire' I was told. After loads of research I discovered it had the WRONG alternator fitted and would NEVER work.
The front brake had the wrong seal in the master cylinder, so it worked as long as you bled it upside down and back to front every few hundred miles.
I actually wrote a story about the bike at the time, got a guy to post it on the web, if you're really bored one day......
http://gazette9.com/pbsr.htm
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I just had to stay and watch as he tried to weld this nut on, with the sump on the car still 