Abnormalities in the accessory drive system (serpentine belt) and/or components may cause an engine RPM variation and possibly lead to a misfire (diagnostic trouble code) DTC. A misfire code may be present without an actual misfire condition. Replace the drive belt, and have the Drive Belt Tensioner inspected also.Worn, damaged, or mis-aligned accessory drive components or excessive pulley runout may lead to a misfire DTC. A loose flywheel or crankshaft balancer can possibly set the same or similar DTC as a misfire, even though plugs, wires, and coils are in good condition. I would also suggest you have your vacuum lines inspected for wear, missing, or dry-rot.
Hope this Helps
A. J. Valle
A misfire can be very serious and can ultimately cause a roadside brakedown and serious damage. The best way to know what's causing the misfire is to run a diagnostic with a code reader or scan tool. The CarMD Vehicle Health System is an easy-to-use product that lets you diagnose check engine light problems -- including misfires -- yourself. It's also a good idea to have your vehicle inspected by an ASE-certified mechanic that you trust. If it's not the spark plugs themselves, it may be the ignition coil(s), which are a very common repair. But don't guess. Know for sure!
〉 Answered on Jul 18th, 2012 by Kristin Brocoff, Director of Corporate Communications at CarMD.com
If you have new plugs and wires that still doesn't mean that it's getting proper spark. A misfire could also be caused by a fuel problem.
You should get a check engine light. Get the code read and then you'll have a better idea where to start. Make sure that you have a technician properly diagnose this condition so you don't end up replacing parts you don't need.
〉 Answered on Jul 18th, 2012 by Lori Johnson, Owner and Instructor at Ladies Start Your Engines