Question about used car engine and trans

I test drove a 92 Camry, which when it warmed up started making these 'pops'. The only thing I could relate it to was an old something or other that had a mechanical fuel pump that was leaking into the crankcase. It exploded every so often. But this Camry did it every 20 seconds or so.
Another 93 Camry I drove had a smooth idle until I put it in gear - then it was really rough - curious about that too.
Same car, when I pushed the OD button on the auto shifter - it wouldn't shift at all - it's not supposed to do that is it?

http://autotechsonline.proboards.com/thread/1958/question-used-car-engine-trans