can anyone help with this problem. i have a 06 f 150 4x4 5.4. it has 140000 miles. i have a miss from idle and during fast acceleration. the miss is very bad when the engine is under load like when the overdrive is on and i am crusing, however if you turn the o/d off and the rpms go up it gets better. so far i have changed the plugs,fuel filter, and mass air meter. it was not reading any codes so today i tried flooring it to get a code and it gave me a p0300 random missfire and a p1000 system check not complete. i have checked for vacum leaks and found none. also if the engine is not under load it seems to not be as bad. i am wondering which of these problems you guys think it might be

cats
coils
vct selonoid

also the truck has a k&n intake and superchips programming and i have always ran mobile one 5w20

 

i would look at coils. sounds like a bad coil especially when you say it get worse when you put it under load.

 

thats what i was thinking but i would think the error code would have been a specific cylinder and not random

 

Does anyone know how to test the coils