Hi, I keep getting a code P1131 (O2 sensor lean). An occasionalbit of roughidle, recently the (4.0) engine is slow to warm up otherwise runs well. Exhaustsmells eitherfuel rich or (ugh) contains coolant, it's hard to tell as the engine is running colder than normal and my fuel contains 10% ethanol. I successfully replaced the O2 sensor about 6 months / 6K miles ago. New head gasketsabout8 months / 8K agodue to coolant loss out the exhaust.
1) I am not seeing signifigant coolant loss but am concerned that I may be leaking coolant into the combustion chamber or exhaust again at a head gasket. 2) If my recently cold engine is simply a bad thermostat,could it cause the o2 code (from low coolant temp) or conversely is the lean / rich mixture causing the slow warm up? 3) My fairly new Bosch O2 sensor might have just gone south for the winter??
Please share your thoughts. Thanks, Kevin (97 Aerostar E4WD &97 Escort Wagon w/over 350 K miles between the two of them)