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!!

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Handyjay