I have a 89 S420 that for it's time it has run excellent. I think my wife's been putting a cheaper gas in it to save money.

Now it has a problem idling. I have run two cans of Seafoam thru the gas tank and the performance is 70% better at idle, as long as there is sea foam mixed in the tank.

A fresh tank of 93 octane from Chevron and the idle is rougher. With Seafoam better, with out poorerand idles about 600-700 rpms.

I want to know if a Oxygen Sensor change could help?

Working, money was no object, Retired now with Obama, moneyless and poorer.