antifreeze is most common problem related to petrol engines misfiring. this can be cured by replacing the timing belt in addition to the thermostat and coolant temperature sensor. this will remedy 95% of misfire problems on most modern cars.
When the engine is cold or when it is misfiring.
It depends on the reason that cylinder is misfiring. It could cause serious damage to the catalytic converter.
Timing belt. misfiring engine
A sparkplug misfiring.
You can but it is not a good idea. If your engine is misfiring then unburnt fuel will enter the exhaust. This will damage the O2 sensor and eventually destroy the catalytic converter costing you big time. Stop driving the car until you can have it repaired.
If your car is misfiring then you will need to get a tune-up. If you don't you will continue to burn excess fuel.
Check your engine timing, it may be too slow.
Misfiring in a car when it is cold can be caused by several things. The mist likely causes are a bad head gasket or a leaky fuel injector. Either of these can allow fluids to slowly mix overnight and the car will misfire until the excess burns off.
most likely misfiring cylinder(s) and/or worn engine mounts.
If your car shakes while underway, your tires have worn incorrectly from misalignment. If it shakes while in park or not moving, your engine is misfiring.
You engine is probably misfiring. Check your ignition and fuel systems.
Usually a sputtering muffler means that a new catalytic converter is needed. The sputtering sound is the car misfiring.