A loose or corroded ground terminal on the driver's side of the cylinder head can cause a rough idle, misfires, and there may be trouble codes. Restore the ground to the cylinder head.
Car Problem Reports
Mazda Protege Idles Rough, Misfires, and Possible Check Engine Light
Mazda Protege Problem
Engines Affected: 1.6L 4 Cylinder, 1.8L 4 Cylinder
Average Mileage: 143,666 mi (60,000 mi - 243,000 mi)