i own a 2006 f150. I've added a cold air intake, e3 plugs, street fire 45,000 volt coils, sct tuner, and I've opened up the exhaust. If I'm in park or neutral and I hold the engine at 2,000-2,500 rpms I have a constant misfire but the computer does not through any codes saying there is a misfire but i can hear it and feel the stumble. It stumbles during idle as well. Also note it did this misfire before the new plugs, coils, and tune. I added those to try and fix it but it didn't work.

 

You aren't going to like hearing this, but pull all that aftermarket crap and put the stock intake back on, remove the tune, and put Motorcraft plugs and coils back in it. Denso is an acceptable alternate coil, they make the Motorcraft coils. Then throw some Techron in the gas to clean the injectors.

If you run an aftermarket intake, you MUST get a CUSTOM tune for that specific intake, not a canned tune. Otherwise it will run too lean and burn valves. This may be your problem if you have been running that intake for a while.

 

I second on glc's remarks.