I am constantly getting a code 11 and sometimes a code 15, 18. even after resetting the code, the fault 11 will appear within minutes. if I just leave it on, a and go to reset it a few days later then one or the other codes show up. could it be my O2 sensor? right now my car has 271,000 miles on it and here are some things that could be related that I have done:
Bosch O2 sensor replaced. Done on 10/7/09 @ 246,939
Check air valve. Done on 10/9/09
Bosch H9DCO Spark plugs 6 total. Done on 10/6/09
*Bosch spark plug wire
set. Done on 10/6/09 @ 246,560
Air pump diverter valve replaced 10/23/10
*Overload Protection Relay replaced 7/9/10

Does anyone think I need a new O2 sensor? my car also cuts off on me while I'm driving.....not often, but its usually when I'm slowing down to a stop. not sure if there is any relation to the cel. and by the way, I do know what the cel code are, but I don't know how to correct them.

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1990 190E 3.0L