I have a 2005 f150 king ranch 5.4 3v had all the timing components replaced about 8 months ago truck runs great but when motor got warmed up it would have a bad idle ( almost like it was camming) would almost die and the run rough unless you hammered down on it. Then here in the last month I have had the idling problem constantly but if you drive down the road it runs fine until you let out of gas. Any help or tips appreciated! New to this but thanks in advance.

 

I'd recommend cleaning the throttle body with the appropriate cleaner. I'm sure the battery was disconnected during the replacement of the timing components and the idle couldn't be relearned because the TB is dirty and not functioning properly. It's a cheap and easy first step.

 

Hey there, this sounds like textbook coil on plug. They could have been disturbed after the timing job.

To confirm, run the truck so that it is idling bad. Then unplug coil on plugs one by one for 4 seconds each; plug them back in before you move on to the next. If one makes no change to the engine while unplugged, you know its bad.

Use your best judgement. Let us know!

 

Not trying to be a smarta$s here, but have you actually tried this. It's not even reliable on a good idling one. The computer on these vehicles is TOO smart for those ole time procedures of by gone days. The PCM is able to detect an electrical circuit problem on the unpluged COP, and 'instantly' shut down the COP on the opposed cylinder in the firing order - and run on six cylinders with such minimal change you can scarcely feel a difference. You MIGHT see a slight difference in RPM if you are monitoring with a scanner - but the PCM will even adjust the throttle position to try to avoid that. Actually unpluging one 'misfiring' due to bad plug instead open primary circuit, it might even feel like it smooths out.

EDIT: For OP. I would ask - Did you drop pan and clean out plastic guide debris and oil pump pickup screen. Did you replace Oil Pump. A 'possible' cause of rough idle might be degraded oil pressure due to air bubbles developing in oil from cavitation by an obstructed pickup screen. Or just age / wear / lower oil pressure that cannot keep / hold phasers at full advance during low RPM idle.