Contour Enthusiasts Group Archives Forums General Troubleshooting Occasional misfires only on startup

At the beginning of May, I received a P0302 (Cylinder #2 Misfire detected) while starting the car up. I cleared the CEL and a few days later received P0420 (Catalyst system efficiency below threshold (Bank #1)), which I cleared as well.

For almost two months I have received no CELs.

Then last Monday, I received a CEL once again while starting the car. I didn't get a chance to pull the code until the other day. I got a P0303 (Cylinder #3 Misfire detected) and a P0420 (Catalyst system efficiency below threshold (Bank #1)).

What would cause the #2 and #3 cylinders to misfire on startup only?

FYI: Plugs and wires should be good. I replaced the spark plugs w/ Autolite APP764 (double platinum) plugs and wires w/ Ford MotorSport wires.