1999 ranger random cylinder dropout

[Cemeteryxgates]

99 ranger with 3.0 flex. I use this truck as a yard truck and sometimes disconnect the IAC to save in fuel and when it runs for about 45 minutes at the low rpm a cylinder drops out and starts smoking almost like a valves hanging open and won't go away until I run it around at 30-45 mph and the cylinder slowly comes back online. any ideas?

Tldr: IAC disconnected for 45 minutes a cylinder drops out and slowly comes back online with high rpms possible valve hanging?