So I’ve had this truck for 3 years 01 f150 4.6l and it’s been a awesome solid truck, but I’ve always have had this rough low idle in gear that I can’t seem to figure out. I’ll list all the symptoms and information below

-cylinder 3 and 6 miss ( it will only throw the miss codes when idling in a parking lot or stoplight ) when driving they will not come on
-rough idle in gear worse when it’s hot outside
-I get some light smoke on start up but goes away
-when in extreme cold temperatures -30cellcius or colder we’re I live during the winter it will backfire a few times after start up then it wont backfire all day.
- truck has had cats removed before I even bought it (o2 sensors are still there )
-On a cold start my idle is perfect but when it warms up that’s when the problem starts

truck has been taking care of its whole life I’m the 2nd owner and he also had the same problem.

I’ll add , were I live emissions laws are not enforced.

thanks for any input.

Yes sorry forgot to add that , coils are new and so are the plugs, fuel filter and DPFE sensor have been replaced aswell. Egr valve is original and most of all the vacuum lines are original aswell. Intake manifold also has new gaskets that i replaced last year due to a leak.

And I’ve done the head gaskets and timing chain also

Motorcraft coils and plugs , and those are the only codes I got , I changed the DPFE sensor when I threw a code for it and it never came back

Okay thank you for the input really appreciated , I will do that and get back to you with the results