Pontiac recommended changing the spark plugs in the 1999 Sunfire every 100,000 miles, and in the process of replacing the spark plugs, you should inspect the spark plug wires for damage and replace them as needed. Pontiac recommended a specific type and brand of spark plug and plug gap for the Sunfire's 2.2-liter engine, but you can go with a different brand as long as the gap and type still meet the requirements.
For the 1999 Sunfire's 2.2-liter engine, Pontiac recommended No. 41-948 AC Delco spark plugs, or an equivalent double-platinum plug from a different manufacturer. The gap between the electrodes on the plugs must be 0.05. Double platinum plugs are not adjustable, so do not attempt to adjust the gap on any incorrectly gapped plugs -- exchange them for new ones.
