Any Ideas!

New to forum. First post.
2003 F150 5.4L Screw 32,000 miles. Been happening for about 2 weeks. Engine idles a little rough about 90% of the time, but the other 10% it's so smooth I would not be able to tell it was running if it wasn't for the Flowmaster. Monday CEL light came on for 2 or 3 minutes and then went off. (cylider 1 missfire) Cleared code and it has not came back.

Also is the Lightning muffler any different then stock muffler. Have friend that will give my stock lightning exhaust.

COP?

K&N drop in, 3.55LS, Flowmaster catback SI/SO, Lots of chrome, Captains Chairs, 285/50's on 20's. 1200 watt audio, Heavy duty tow package, Wood Dash kit

 

rough idle id suspect I.A.C valve.

 

"Cylinder 1 missfire" can you feel it miss under heavy acceleration? If so I'd put my money on the C.O.P.

 

Under acceleration runs great. I cleared the code and it did not come back. Its not a constant rough idle. It will run smooth stumble a few times and run smooth for a few seconds. Also my gas mileage seems to be going down.

 

I bet before long it will start missing under load...if it wouldn't of had that cylinder one misfire I might think different but I have had that damn code 4 times now and the C.O.P. has been the culprit each time....

 

It was the I.A.C. THANX.

Changed the plugs too while I had the ambition. Not as bad as everybody says it is.