I had the test run yesterday on my S500-184K miles. I have had the check engine light on now for nearly a year. When I reset it and travled out of town it stayed off but once I was back intyown and setting in traffic it would come back. The mechanic yesterday said that I needed to chance out my 4 oxygen sensors they recommend every 90K miles. The ones on the auto are the original. The mechanic said that the test showed all of the oxygen sensors to read slow just barely above minimum.
He also said my air pump was working great opening and closing as it should.
But that where hte air flow goes thru the engine that it was partly stopped up with carbon. His suggestion was to have the carbon cleaned $4K and replace all for oxygen sensors to get a stronger and better running machine. My questions are as follows;
1. Should I replace the oxygen sensors being the mileage- I can DYI with OEM for less than $400?
2. Is there a DYI for cleaning the carbon?

Thanks for the information,
MBD