Chrysler Repair: Town and Country 3.8L rough idle, shade tree mechanic, town and country

Question
Please help. We purchased a 2001 Town and Country with a 3.8, last week from a used lot, as is. It has 156000 miles which made it affordable. The engine run strong and the transmissions shifted great, it was very clean and seemed to have been well cared for. The day we purchased it we drove the hour trip home with no problems it run great. The next morning it ran terrible. Wouldn't idle without giving it more gas, the check engine light came on. We have a small code reader. The codes were rich fuel, multiple misfire, 2&5. So I started with the plugs then the wires. That seemed to fix it, drove great the rest of the day, next day rough idle and multiple misfires but haven't had the fuel code anymore. When its running good the compression is good. Talked to a local shade tree mechanic who said that he had seen this before told us to replace the ignition coil. Our local parts store didn't have it in stock but the car was running good so we drove the hour trip to get one, the car did great. At the parts store the clerk who was holding to part for us came out and listened to the car, had us shut it off, he pulled the number 2 plug wire and had us start the car. He said its clicking so it has spark and there is nothing wrong with the coil. He recommended a shop across the street to look at it so we went. That mechanic was very nice, he listened to the van then to our story and said it is the coil. He said he has seen this before and when they start to go bad it will cause the problem we are having. He said he was sure because it was always 2&5 and it was intermittent. So we went back across the street and purchased the coil, drove home and installed it. The car ran fine but was running fine before. The next morning, ran great. The next morning, rough idle, multiple misfire on 2&5. I don't know where to go from here. The only correlation that is obvious to me is that the temp is cold when it is running rough and warm when it runs good but since we've had it less then a week this may be a coincidence. Please help if you can. Thank you, judy

Answer
Hi Judy,
When you rough idle when starting up the engine from cold my suspicion is either that the temperature sensor of the coolant is inaccurate which should set a fault, or that a part that is not so easily sensed as being faulty: the exhaust gas recirculation valve.
My suspicion is that your egr valve is sticking slightly ajar which will cause the engine to falter at idle speed or be hard to start. The valve is located near the throttle body air intake at the end of the engine, mounted in a small diameter pipe that recirculates exhaust gas from the rear cylider bank exhaust manifold back around to just below the intake manifold where the air from the filter enters the throttle body. The exhaust gases have some fumes that can plate out a crud on the valve stem and thus keep it from closing tight when you are start or at idle. That makes for a too lean mixture so the engine stalls. The valve proper is mounted horizontally with the stem visible in a space between the body of the valve mounted on the pipe and the round top of the valve which is flanged and so if you look carefully you will see a metal rod (stem of the valve) with a slot around its circumference. You can take the tip of flat blade screwdriver and insert it in the slot and then lever the valve back and forth to check if it is moving freely (against spring action in one direction) or not. If it doesn't seem to close easily with the help of the built-in spring, then I would spray the base of the stem with solvent from a pressure can (such as WD-40 or carb cleaner) while moving the stem back and forth. See if that makes it run better upon starting.
If not, then you would want to check the resistance of the coolant temp sensor located next to the thermostat housing on the top of the engine near the front. The top radiator hose attached to the housing, and the sensor is next to that. You would need a volt-ohm meter to measure the resistance. When it is cold it should read in the range of 15,000 to 25,000 ohms (or even higher if it is very cold). If it is down below 10,000 if the temp is below 32F then it is off-value and causing a too lean mixture.
Roland