My 03 Xterra SE (150k miles) has a rough idle and continues to drive rough. I have not accelerated past 40mph but it is consistently rough throughout driving. The Service Engine Soon light flashes, too. But, no code registers when I scan for it. I have taken it to Autozone and Firestone but neither of their mechanics could tell me anything. The rpm at idle is normal and the temperature is normal according to the temperature gauge I replaced the spark plugs, air filter, changed oil, and filled up all other fluids about a week ago before any problem arised. Any thoughts on the problem? Is it dangerous to drive with the SES lashing?