Dodge Repair: chrysler lhs, intake manifold gasket, chrysler lhs

Question
doug i have a 1995 lhs that runs rough at all speeds and temps .obd shows 12. that would be from running battery down but this was going on befor that happened there is no check engine light on or ever was.. its almost like there is a bad vac. leak any ideas would help thanks  

Answer
What's the history on the plugs and wires?  

Also, the 3.5L v6 had problems breaking intake manifold bolts as well as sucking in air at the intake manifold gasket.  This is not to be confused with the plenum which is the big aluminum component that looks like an E and 3 (E3).  However, a blown plenum gasket can contribute to this as well.

Sometimes I've seen EGR valves fail as well which will give a surging type feel going down the road.  
Doug