Hey guys,

I haven't been online since I fixed my misfire problem by replacing plugs about 25,000 miles ago. I had no issues for a while and the truck ran great.
However, lately the truck has been idling rough. It happens in gear or in neutral. The weird part is that sometimes the truck idles around 600-650rpm in gear, and it idles rough. But sometimes the truck idles at 500rpm in gear and it idles perfectly smooth.
It has a slight tick at idle but using Forscan I can see the phasers both stay under 1% error at idle.

Any idea why it actually idles smoother at the lower rpm? Most threads I've read people have the opposite issue.

 

To add some more information:
The IMRC system is working.
The truck will rarely record a misfire on cylinder 1, 4, and 8. Not all at the same time, just occasionally one misfire on one of these cylinders.
No codes stored.
MAF has been cleaned.
Throttle body has been cleaned.
Plugs replaced 25k ago along with a bad COP.
Fuel filter has not been replaced, fuel pressure is 270kpa at the fuel rail according to Forscan.

 

Change Coil boots and springs too?

 

No not yet, I don't see why it would idle perfect at 500rpm if they were bad but for $35 on rock auto its cheap enough to try though. Thanks for the suggestion.

 

Sometimes moisture can cause corrosion inside the coil housing where it mounts to the contact. They can also ground out if they’re worn out and not insulating properly. You seem to have already performed most of the standard troubleshooting, changing that fuel filter wouldn’t hurt either if it’s been a while.

 

Bumping this post from the dead to provide an update for anyone searching for this issue. I just logged onto this site for the first time in 5 years.

It was a couple of bad coils as suggested. Cheap china ebay coils fixed my issue. Truck was going strong at 180k miles when I sold it. Still going strong now well over 200k miles reportedly.