When a car engine is acting up, the best way to address it is to narrow down the specific problem, whether it's a sound, smell or other symptom, use that to narrow down the cause, and then determine if it's something that can be fixed at home. Troubleshooting a car engine requires taking a lot of variables into account, but it's important to at least investigate any strange smell, sound or engine reaction.
Many car issues are indicative of specific problems and can be diagnosed easily. This may be as obvious as an oil puddle under the car indicating that there's a leak in the seals or a rotten egg smell coming from the exhaust, which often indicates the coolant is too low or the coolant system is not working. Some individual issues may not narrow the problem down as much, such as white smoke from the exhaust, in which case it's best first to investigate the easiest problem to reach. It's much easier to see if the cylinder head gasket is bad than to replace the engine block, for example, so rule out the easy fixes first.
If tracing the symptom back to the cause of the problem is difficult, websites such as AutoMD offer a question-and-answer diagnostic tool, as of 2015. By reporting the problems to a diagnostic website, a problem the person had not initially considered may pop up. This is a good option when the problem is uncommon or does not have an obvious cause.