2003 Ford Taurus DOHC, 100,000 miles: After the engine runs for about 2 minutes at idle, the engine shakes and surges, rpm varies at idle and eventually stalls. At driving speeds engine runs fine, plenty of power. Engine light on. Codes P0171, P1151 & P1131. Running lean? Shortly before this problem developed put in new air cleaner, fuel filter and spark plugs. After problem put in new wire set, upper oxygen sensors and cleaned the mass flow sensor. No obvious vacuum leaks. What can be the problem?

 

Sometimes in the process of servicing, we disturb something, I would suspect you have a hose off somewhere because the computer adjusts fuel according to inputs from the air flow sensor, among others. It seems that extra air is getting into the system that the air flow sensor is not accounting for. A thorough recheck is called for including the wires too.