Chrysler Repair: 1996 Chrysler surges, camshaft position sensor, intake manifold gasket

Question
Car 1996 Chrysler LHS 3.5l 81,000 miles
History: Car had rough idle (suspected Intake manifold gasket) previous Air Idle Control fault (shorted winding), fault went away. Timing belt failed replaced aprox 20 k miles ago. The car was driveable but got worse last year. Inspected and replaced plugs and it ran better for a few weeks. Recently it began to run worse and I noticed a surging and slight smell of fuel sometimes when I shut it off. I knew of the problems with the intake manifold and fuel rails on this car so I started repairs.

Repairs: I inspected and replaced the intake manifold gaskets. It definitely was bad by cylinder number 5. Upon reassembly I noticed a 'wetness' around one of the injectors. I replaced the Air idle Control. The car idled much better but there was still a surge when driving and the car would 'buck' when at highway speeds. I noticed a fuel smell.  I tore it down an replaced the injector o-rings, they were definitely bad. While I had them out I cleaned them with injector cleaner. I had trouble getting an o-ring for the fuel line to fuel rail. I put a OBDII computer on the engine. I notice a slight tremble in the engine rpm and vacuum that coincides with an erratic timing advance at idle. the fuel trim and O2 sensors seem to be running normal even though one fails to report a voltage occasionally and will cause a check engine light. (only twice in several operations) I suspected a timing belt was about to fail so I tore the front off and found out that the timing belt and water pump were like new and the timing alignment marks were right on the money. Since it was cheap, I replaced the camshaft position sensor. I replaced the PCV valve and hose. I plugged the vacuum lines from the Evap recycling system and the problem didn't go away, in fact the engine caught fire. Fortunately, I had anticipated the possibility and put it out with a fire extinguisher without any damage. I have also replaced the passenger side motor mount and the transaxle mount because it seems like the engine would be bumping the hood sometimes. This bumping was an old problem that I tolerated.

Question: Is an erratic timing advance normal at idle? If not what else could cause it? The timing seems stable upon acceleration but gets erratic again when I let off of the gas.

Answer
Yes, the timing will float a bit at idle. I've never gotten an answer as to why other than its trying to keep emission output low. In your case, I would focus on the O2 sensors. If either of the upstream sensors is failing or operating slow the engine will surge and buck.