Run some Seafoam through the gastank. Cleared up my check engine light on my '05 Altima SER. I also got a Duty Cycle Meters from Sears and adjusted my air/fuel mixture on my 300E (do a search for how) which, if out of adjustment, may cause issues. I live in OC, Ca. Have 195K on my car. When I bought it, it was running and idling like crap and struggling to start. No issues now (well, except for the delayed reverse and drive engagement which Ps2cho has a detailed fix for on his website...thank you in advance!). Also, spray some contact cleaner into the steering wheel space behind the airbag and might fix your SRS light. Mine was coming on a lot and I did that...nothing in 6 months so far!

Steve