Chrysler Repair: Concorde 3.5L 97 rough idle 12-43-21-21, oxygen sensors, obd ii

Question
Roland my car has a rough idle when it is in gear. I read codes 12-43-21-21, I read earlier the codes don't duplicate but I read these 3 times and 21 did repeat. I also read in an earlier post the erg valve could be bad, would you replace the O2 sensors as well(are there 2) Thanks for your help ! Jamie

Answer
Hi Jamie,
My inclination would be to get a code readout using a plug-in code reader so as to get the four digit fault codes that are associated with the OBD-II system. Most Autozone parts stores will do that for free, or an independent garage should be able to do for $40 or less. Your vehicle should have that system too, as it was supposed to be on all vehicles by '96 (unless the car was originally delivered outside the U.S.?). The double 21 does suggest both oxygen sensors though I have no confirmation on that score, but in any case each bank of cylinders has a sensor.
I would begin by lubricating the stem of the egr with some WD-40, where it enters the valve body. That may be enough to free up the action at idle so it closes firmly, and enriches the mixture properly. That could solve the idle issue all by itself. With a better readout too you might be able to focus on which of the three coil sections is giving the 43 code, and then focus on that one.
Roland