mercury villager 1999 random multiple cylinder misfire

[moshawh101]

I have a 1999 mercury villager that is showing a random multiple cylinder misfire code and an o2 sensor code. The vehicle has a small leak on the exhaust between the catalytic converters and I'm not sure if this would be affecting the back pressure enough to make the engine throw these codes. Also I replaced the distributor and tried the original placement of the distributor and multiple placements. I am going to get the exhaust fixed and put either b12 cleaner/ seafoam cleaner through the engine and fuel system to see if anything will clear up the fuel system/ make it slightly better. The vehicle runs rough at an idle but runs smooth when reving and at higher speeds above approx 1300+RPM's. Are there any other explanations to why it would be running rough?