Chrysler Repair: concorde idle and shadow tach, ac voltmeter, propane torch

Question
I own a 92 dodge shadow es with 3.0 v6, and the factory tach stopped working.  I cant seem to trace the wiring to repair it?

Also, I have a 1997 chry. Concorde.  Has 3.5L all options except ABS. Engine light came on, ever since will not idle below 1500rpm. Tried replacing air plenum gaskets, Egr and gasket, plugs, wires, and tried running propane torch (unlit) around top and intake of engine.  Idle did not drop, sputter, change etc. If I unplug battery and let sit for hour or 2 will start, run perfect and idle fine for little while, but once warm trips engine code "running lean" and idles up again.  Uses way too much fuel (only getting about 14 mpg mixed driving) but otherwise doesn't run too badly.  Oxygen sensors become clouded with white chalky substance quickly, but head gasket is fine, had checked. No fluid transfers between anti-freeze and oil or vice versa, and no other real problems.  Car has about 120,000 miles on it, and had to other mechanics which cannot help me.  Please help or its off to the scrapyard.  Thanks.

Answer
Hi Jerry,
The tach gets its signal from the distributor via the pin 43 of the engine controller on a gray/light blue wire to the cluster at pin H of the gray plug. You can check as follows.
Remove cluster bezel (4 screws), remove mask and lens (5 screws), remove cluster.
Check for 12v at pin J of gray connector, check for 12v at pin K of gray connector with ignition switch in run postion, check that pin F of red connector is grounded.
Using an AC voltmeter check that you have at least 1.0 volt AC on pin H of gray plug with engine running. If less than 1.0 volt and pin H to pin 43 is patent, then replace engine contoller. If more than 1.0v then replace the tach drive module at the edge of the circuit board by lifting edge and pivoting away from locating pins. If a new module doesn't fix it then replace tachometer itself.
Most likely you need a new tach drive module which is a standard replacement part from a dealer or maybe you can find one in a wrecking yard.
On the 3.5L if your code was "fuel system running lean", then the possible explanations are several:  upstream
oxygen sensor failure, fuel pressure regulator, fuel filter, fuel pump, MAP sensor inaccurate, injector leaky, leak between exhaust manifold and downstream oxygen sensor, coolant temp sensor off value. Those are pretty extensive  and exhaustive set of tests to run, I know, and that you have already spent on these sorts of tests. But maybe you have a sense of which might give you some pay dirt and focus upon those. Tell me which ones you want to run for which you don't have the specs. It gets my attention when you threaten "off to the wrecking yard"! I wish it were a simple solution.
Roland