When your vehicle is acting up in any way, you don't want to ignore or overlook this problem; small problems can soon turn into major repairs that need to be done under the hood, and your car could literally shut down while you're driving, depending on the repair that's needed. You could also be jeopardizing your safety or the safety of others if your car is not in good repair while on the road. Note some seemingly minor problems with your car that might not be so minor after all, and why you need to get these addressed as soon as possible.
Sputtering and stalling
If your car's engine sputters and stalls, you might assume it needs a tune-up. This can be true, and a new air filter and spark plugs can get the engine running smoothly again.
However, an engine running rough like this can also mean a number of problems that keep it from maintaining proper combustion, so that it sputters and even stalls. The oxygen sensor may be failing, so it can't note how much oxygen should be brought into, and then filtered out of, the engine; the oxygen boot, which fresh oxygen travels through, may be split or damaged. The fuel pump may be failing, so that there isn't enough fuel being delivered to the engine. These problems will just get worse so that the engine eventually dies. Have this seemingly minor problem properly diagnosed to avoid this risk.
You should never notice exhaust or any type of "dirty" smell from any part of your vehicle, other than the exhaust pipes themselves. If you notice this smell from under the hood, don't assume that the engine is just burning contaminated or low-quality fuel. This smell can mean that there is an oil leak under the hood, and the oil is burning as it drips onto the hot exhaust, creating this smell. Oil could also be mixing with fuel as it reaches the engine, causing a heavy or exhaust-like smell. This can be damaging to the engine, as it needs to work harder to create combustion with oil in the piston chambers.
Smelling exhaust in the cab can also mean that there is a leak in the exhaust system, allowing fumes to vent into the cab. This is very unhealthy for you, and can also mean that some of that exhaust is backing up to the engine, causing it to work harder. Don't assume this smell is something you can ignore, but have the exhaust system checked as soon as possible.