Q: Car overheating and running rough

A rough idle can be caused by many things. Something as simple as a bad spark plug wire or bad coil can cause a vehicle to idle rough. Since you have an overheating issue as well while driving, the problem may be more complex.

Overheating and a rough idle that happen at the same time can be caused by a blown head gasket. A blown head gasket means that the cylinder is not sealed, so the compression from the bad cylinder leaks into the cooling system. This causes a rough idle because the cylinder is not working properly.The hot compression gasses that leak into the water jackets heat up the coolant and the radiator cannot cool the engine down fast enough causing it to overheat.

Because diagnosing blown head gaskets requires special tools, I would suggest seeking help from a qualified mechanic, such as one from YourMechanic, who can help you diagnose why your car is idling rough.