OK... update to my last post...Originally Posted by matt5112
First, I mistakenly said the miss was most noticeable in "closed loop" (warm up) mode. Apparently the warm up mode is open loop. And once I got on the same page as my mechanic he said "COOLANT TEMP SENSOR"|". He said the computer won't throw a CTS code until the temp reading is zero. So if the sensor is sending erroneous temp to the computer it will mess with the fuel flow and make the engine run rich and rough. Why the problem seems to manifest itself with a miss and code in #4 is a mystery.
I replaced the CTS ($16) and the 3.8 is now running smooth as a baby's butt and NO SEL! The CTS is directly under the top radiator hose on the intake. You need to loosen the serpentine belt to get to it with a 3/4" deep socket.
I don't know if this will cure ALL the #4 misfire problems, but it sure sent mine packing in a hurry. ~FH
