When you car engine sounds rough after the car reaches high speed.
Car Problem Diagnosis
A car engine that sounds rough when a car reaches high speed is an indication of a problem on spark plugs or spark plug wires, as you can see when you drive faster the spark plugs fires frequently which make the spark plugs or spark plug wires put to a maximum use at high speed, at this condition the rough engine sounds is noticeable when the spark plugs or spark plug wires are failing.
Possible Cause of Rough Engine Sound at High Speed
Spar plug or spark plug wires problem
How to Fix Rough Sound of Engine at High Speed
This kind of problems in most cases can be fixed by replacing the spark plug and spark plug wires, any auto parts store sell spark plugs or wires so you have an option to shop around for the best price, also when you want to replace the parts your self just refer to a repair manual that covers your car model. However, if the problem still occurs after the replacement of spark plugs or wires, then the only option is to bring your car to a reputable auto repair shop and ask the mechanic to conduct a complete analysis of the problem.