Help! E320 'check Engine" light problems

I hope someone here can help me. Despite running perfectly, the "Check Engine" light on my '95 E320 came on and was diagnosed by the dealer as a
bad o2 sensor, which they replaced (for $350). After resetting the computer, the light came back on within a week. Does anyone have a clue as to what might be going on here? Perhaps a bad sensor installed (they say it was checked and operatring fine)? I distrust the dealer and would love to have some insight before trying to get this resolved. Many thanks in advance.
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What was the fault code? A lot of times, shops do not research the fault code and just throw an O2 sensor at it!

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Thanks for the repsonse. Unfortunately, they didn't give me the code; only the service bill. I am getting very sensitive to this because they have replaced both the o2 sensor and the air mass meter in the past 4 months and the problem persists. Any other ideas?

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I'm was having the same problems w/ my 98 E320 61,000 miles on the clock.
Changed the gas cap and it cleared up.
.

"Check
as
clue
love
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Your car is OBD1 and therefore you can get the faults codes that are tripping the CE lamp. Post that code here and we can help you.
Code access is gotten from the Diagnostic Connector box in front of the battery
Simply , with the key on , hold the push-button switch down and a red LED lamp next to it will light. Hold for 2/3 sec. This initiates code retrieval.. Release and the led will flash backcodes. Count the number of flashes. Repeat procedure again for more codes . The will come up in numerical order .
Post the number of each sequence of flashes and we can tell you the code meanings/remedies. PS= If only one flash comes back, there are NO codes stored [ which can not be the case in your car as the CE lamp is on -meaning a code has been detected
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DR, I just wrote to the NG regarding this same problem, but the vehicle turned out to be early 80's and a different problem. I had this problem with my 1997 E320 and had two potential resolutions;
1) A bad or leaking (same thing) gas cap. - replaced cap for around $12 - no difference. 2) An Air Mass Meter going bad. Along with the "Check Engine" light I noticed the car would bog down some on hard acceleration. This got progressively worse. - a mechanic checked the device and found it faulty - I replaced the Air Mass Meter - the light went out and the car runs great.
The Air Mass Meter is located between the air intake and the air filter housing, right in front of you as you look down at the large air fittings. It is easily removed - the hoses on each end pull off after loosening the clamps and the unit has an electrical connection that you unplug. Slip the new unit in and plug the connection in. The whole thing is a 10-minute job. I would make certain the unit is the problem - at MBZ the unit was nearly $350. At a local parts house I bought the unit for about $170.
Good luck with this, Ken
DR wrote:

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