I recently had my 120,000 mile service done, at that time my check engine light was on for multi cylinder misfire (2), Courtesy Nissan thought the problem would be solved with new plugs, part of the service. About two days later, the light came back on, another misfire.

My question is: what else can I do to prevent these misfires??? There is not much mention in the above discussions.... Any help would be appriciated, Thanks.