M.B. Doc,

Thanks for the reply.

1997 S500 112,000miles

The car became rough at idea. I had a friend take a look and he was thinking I may have two problems. 1. an O2 sensor issue and 2. a fuel contamination issue.

I changed the fuel filter and added some fuel treatment. At first I tried a Cheveron injector cleaner. Then I used Redline Fuel System Cleaner which seemed to be more effective at improving idle smoothness. The filter change also made a significant improvement.

still getting the P0133 slow response, so I changed out the last two sensors. All sensors have now been replaced with Bosh sensors, no generic splice sensors.

It's late, so I'll look into the vacuum leak / fuel pressure reg tomorrow.

thx