I have an 01 Sable with the Duratec 3.0. I bought the car with 39000 miles and it has 143000 on it now. Happy with the car except in the winter. For the past 3 years when the temperature drops below 30 degrees, the car starts idling rough. The colder it gets the worse it idles. The idle jumps way up on the initial startup, and drops down and lopes really bad. It acts like its loading up with fuel. You can't seem to hold the rpms steady with your foot unless it's above 1500. After about 10 minutes or so, it will straighten up and you are fine until the next morning. I've replaced the pcv valve, I've replaced one split vacuum hose, i've replaced a coil pack, i've replaced the plugs, wires, coolant temp sensor, i've cleaned the maf sensor, i've also replaced the upper intake gaskets. I'm at a loss here. The codes that are coming up are a lean bank 2 code and a misfire bank 2 code. This is becoming a slow process because I fix one thing then have to wait until the next morning for the engine to be completely cold before firing it up and testing it again. I even went as far as taking off the air cleaner housing and forcing hot air in it with a hair dryer trying to trick the computer into thinking it was warm outside and the car quit running on me. I unhooked the MAF sensor connector while the car was idling and it didn't change nothing. It never even set a code when I unhooked it????? Please help,, summers coming and I want this fixed. Thanks.

 

From what I have read you haven't tested anything. It seems you are just replacing parts that might cause the problem. The one exception is the bad vacuum hose you found. You know that apparently the one bank is running lean. My guess it is not a bad spark, as you seem to have replaced all of that. So it is probably a lean miss.

Instead of throwing parts at it, spend the money to have a computer diagnosed done on it. It might be a bad fuel injector, or even a bad ground. Could be a bad driver in the computer. Maybe a bad head gasket that seals up when warmed up. I use to do computer diagnosis & you would be amazed what cropped up. I remember one time the problem was a bad diode in an otherwise working alternator.

Oh one other thing I notice that when you got the car it had 390,000 miles on it, but after three years it only has 143,000 miles on it. I'm it was a typo.