Diagnosing a Mild Ignition Misfiring Problem

If you have occasional misfiring, it could be the fault of dirty spark plugs, a faulty plug wire or a weak ignition coil. But if the misfiring isn’t bad enough to trigger a code, what can you do? Check the LTFT fuel trim readings; slight misfires can cause the LTFT readings to trend high before a misfire code ever shows up.