Can some of the gaseous chemicals in many of the car exhaust by-products of the combustion engine be carcinogenic or cancer-causing?. Could car exhaust behave in a ways that are similar to 'second' hand smoke' from cigarettes that is known to cause many health problems? Can such pollution always be cleaned up or at least 'filtered out'?
Yes almost definitely. Its not just gas, but additives, lubricants/oils, coatings, coolant (some of which leaks into the combustion chamber) etc. The full list of known carcinogens is available here.
Also see the EPA report here which says ...
"EPA estimates that mobile (car, truck, and bus) sources of air toxics account for as much as half of all cancers attributed to outdoor sources of air toxics. This estimate is not based on actual cancer cases, but on models that predict the maximum number of cancers that could be expected from current levels of exposure to mobile source emissions."