Sailaway again, you need to fix your furnace first
Kidding
Is the Engine light on? If it is you need to get the codes read out. Bad coil would usually throw an error code and engine light.
If a cylinder is not firing it can ruin your expensive catalytic converter.
This isn’t the same folks that you had fixing your furnace (excuse me boiler) is it?
Good mechanic should zero right in and not be guessing. That’s why I ALWAYS got to the dealer. They will know the car inside out and sometimes it’s a free recall, like defective head. Save money in the long run. Computer will probably know exactly what’s wrong than trial and error Mike around the corner.
Could be plugs, PCV valve, vacuum leak, bad coil, bad gas, timing chain slipped a tooth, crack in intake manifold, bad injector (if it had them).
Smell of gas is a big hint though and eliminates a bunch.
Is the smell from under the hood or the tail pipe?