Why does it stop in closed loop? I am thinking it is a vac leak or unmetered air causing closest cylinder to run lean. The computer compensating by enriching mixture causing stumbling in other cylinders.
Maybe unrelated but I have been noticing a large amount of water coming out of all of exhaust.. At tips, muffler, ball joint.. Enough to leave puddles under the whole exhaust system..
-Greg
A vacuum leak is a possibility but my thought on that is if its running badly enough to back fire thru the intake to the point it blows the air filter off, it a decent size leak. One that size would affect the engine at any temperature/open loop/close loop. The leaks I ran into when at the runner would either be really bad and obvious because you could hear them and the engine would run like shit all the time, or so small the miss fire was very random and subtle. Temperature and metal expansion could affect the amount leaking but I just don't think enough. I wouldnt rule it off the table but just not what I've experienced in the past.
In open loop the pcm isn't applying what the o2 sensors are measuring. So if there was a vacuum leak at the runner and the o2 sensor was picking up the excessive oxygen, the pcm wouldn't richen up that bank until it went into closed loop. So its kinda backwards to your problem.
Why it does it, or appears to be doing it, only in open loop points me towards the metering being done on the other end. In open loop the pcm is running on base programming maps only being adjusted by what the maf, map/baro, rpm, and temperature sensors are seeing. Its half blind because the process can't really see the reaction to the inputs without the o2 sensor data. So say a maf sensor is giving slightly skewed data, the pcm applies it to the fuel and timing maps and all "should" be well. But when the o2 data starts coming in the pcm see's that its not all well and it adjusts accordingly and engine runs fine/better. But it could also be a problem in the PCM. They do go bad sometimes.
I wouldn't be overly concerned about the water coming from the exhaust. Its most likely condensation. The O2s are mounted so water wont sit and collect on them. And again I don't believe you have a head gasket problem or other issue causing coolant to make it into the exhaust.
