Intermittent rough idle and poor acceleration
 

I thought I solved my 92 300E rough idle and poor acceleration problem but it has returned. It is acting the same as last fall when I replaced the O2 sensor and then engine performed great. Now 5 months later same poor idle and performance but it comes and goes. I replaced O2 with Bosch unit. Do these often fail when new? I thought I replaced the OVR last year but after checking records I did not. Could the over voltage protection relay cause intermittent problems? Stumped!!

When did you replace the fuel filter last? A partially clogged fuel filter can cause the problems you are experiencing. Recommended fuel filter replacement interval is every 60,000 miles.

Have not considered the fuel filter. Only have 50,000 miles but it is still 26 years old. The quality of fuel is an issue. I try to avoid ethanol fuels but not always possible. This car has part time usage as it is stored for 3 months at a time between being driven for 3 or 4 months. Purchased 3 years ago with 35,000 miles. I don't think the previous owner had the filter change but I have all the service records and will check it out. Filter is cheap and I will replace just in case.
Thanks for your input. If it solves the problem I will post result.

92 300E w/ 50,000 miles?!?! The problem is that that car needs to be broken in