Running rough and rich at idle

1992 Comanche, 4.0 HO, 190K miles.

I picked this truck up in January and have been getting just the way I like it. She will run down the highway and gets around 19mpg, which is great. However, when it sits at idle, rather it be in drive or park, she runs rough and is running rich (exhaust smell).

I have done the following to fix this issue:
- Replaced spark plugs and gaped
- Replaced distributor cap/rotor
- Replaced coolant temp sender
- Replaced air filter
- Checked all vacuum lines and caped/replaced as needed
- Checked fuel pressure (32psi at idle)
- Replaced IAC with one from my folks 93 XJ that runs perfect

It is not throwing a check engine light and runs fine in all parts of the power band except idle. During the cold weather it is even worse at loading up. The truck does have a small crack in the exhaust manifold.

Thanks for any tips or suggestions.

A known problem is that the exhaust header lets too much exhaust leak out and then the o2 sensor makes them run rich. Fix the exhaust. New header or weld. Check engine and transmission mounts for excessive play which makes header crack.

Hopefully you saw this one: http://www.naxja.org/forum/showthread.php?t=989330

Thanks for the help. I did read through that post. I am also experiencing lower than normal idle now that the temperature is staying around 70 outdoors.

My motor mounts are garbage and I assumed that was a primary cause with the header crack. Hope to be picking up a set of MORE mounts soon and anticipate getting the manifold welded or replaced at the same time.