Timing and vaccum question!!! Please help

How many degrees advanced should the timing be on a healthy 4.0l straight 6. Mine was reading 7.0 to 7.5 degrees at idle and it just seems to be running a little ragged.
Also, what should the vacuum pressure be on the engine? And how does the vaccum pressure relate to the timing, like, retarded or advanced timing equals more or less vaccum pressure? Thank you for you help.

Using a ScanGuage, the 4.0L at idle when the O2 sensor was bad fluxuated between 5 and 15*. When the engine is healthy it idled between 15 and 17*, ran down the highway at 32 to 37* and go as high as 40* with my foot on the breaks on the exit ramp leaving the highway at 50 MPH or higher.

The year may matter for what the timing is. There are some good threads for vacuum if you search.

Here's a good one. http://www.naxja.org/forum/showthread.php?t=1002311&highlight=vacuum+gage

The correct answer is the timing advance will be whatever the ECU/PCM decides it should be based on sensor input.

I would expect a healthy 4.0 to have a steady 15-17 inches at idle.

[QUOTE=joe_peters;244750646] I would expect a healthy 4.0 to have a steady 15-17 inches at idle.[/QUOTE]


Closest I've seen to a "stated number", thanks. Would that be "in gear" or out?

Been searching around this a.m. for more info on cylinder misfire problems.

http://www.naxja.org/forum/showthread.php?t=1019843

Mine idles at 16.5 with a 0.2 fluctuation. Mine is a 2000.