2001 Dodge Stratus Question: Idles OK in gear, but RPM's pulsate when in park or nuetral,

Car was running good but had oil leak into spark plugs and around valve cover. Replaced the valve cover gaskets, and spark plug caps, spark plugs, and wires. Then had a code for random misfire so replaced distributor cap and button. Now getting a pulsating idle when the car is in park or nuetral, after about two hours of trying to trouble shoot this a new code appeared P403 indicating an issue with the "EGR transducer circuit open or shorted"