E36 Rough Cold Start and bad O2 sensors

Car will start but runs very rough until warm. Large amount of blue smoke on initial start up. How much effect does bad O2 sensors have during cold weather start up (30-40 degrees F)? Car has had history of very small head gasket leak, which has caused the O2 sensors to fail. Do not want to change O2 sensors (again) until I am certain head gasket leak is resolved. (Not trying to get into a big head gasket discussion. I checked compression with very good results, not mixing fluids, no overheating, used approximately 12oz or less of anitfreeze during last 2500 miles. Please no comments about head gasket.) Just would like to know if there is some other major reason car would run so bad at cold start up. Blue smoke may occur with warm start up but car does not run rough unless cold weather. Replaced spark plugs with correct BMW plugs recommended by BMW mechanic. Blue smoke stopped on start up for about 2 weeks. Changed the plugs before cold weather become a issue, so not sure what effect plugs had on cold weather start.

well, without mentioning the headgasket....

blue smoke is an indication of burning oil, which points to either valve seals or rings. either way, the oil burning will also kill the o2 sensors.




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Thanks for the reply

I'd check the gasket that sits between the block, and the part of the engine where the valves hang out. I forget what that part is called though.

The intake and exhaust manifolds bolt onto it.