How long have the spark plugs been in the car?

Maybe, just regap the plugs to spec (check the sticker on the inside of the hood; it might read something like 1mm 0, -0.1mm tolerance which means gap them at 0.9mm).
If the plugs are worn out, replace them (gap them to spec per hood sticker).

Be careful about torquing the plugs the treads in the head are aluminum. (the torque spec is pretty low)

It may sound stupid. But, check all the engine grounds and the car body ground for good connection. Also, a weak battery can cause all kinds of bogus problems.