My 1987 560SEL has an intermittent problem, the oxygen sensor light flickers on and off, the engine hesitates and sometimes stalls while this is happening. The oxygen sensor has been replaced, and this did nothing for the problem. Also the AIR pump cycles on and off when the light flickers. Any help would be appreciated.

Who replaced the O2 sensor? Also, make sure all connections are in place. The sensors come with anti-seize compound on the threads, but if some gets on the sensor. It makes the sensor useless. Get it checked out.