Noticed a slight skip at idle or when cruising at low rpm, codes for 1&8 misfired so we changed the plugs.. Now it says random misfires. Mechanic at ford dealership says this is from using champion plugs.. Only does this at idle .. Revs up fine..Anyone heard this or any suggestions?

 

If the plugs are the correct heat range for your motor & gapped correctly, the plugs wouldn't cause a misfire. If Champion's web site matches the plug part number you installed with your motor, and you gapped it correctly, then the plugs are probably not the cause.

Random misfires usually indicate a system wide problem, like a vacuum leak, low fuel pressure, low battery, bad alternator... The list goes on. Here is a good site on how to diagnose it: http://www.random-misfire.com and http://www.obd-codes.com/p0300

 

Any chance you have aftermarket COPs? They're known for problems.