I have a 2002 expedition. When I start it up in the cold mornings I smell a rich smell, but goes away when it gets warm. Could it be the oxygen sensors? and the service engine soon light soon is on.

 

It could be. And it could be several other things.
The thing to do now is get the code that has set in the computer and obtain some guidance as to which system has the problem. Places like Autozone will get the codes from the computer for you at no charge. Get the code(s) and post them here , we should be able to help guide you in making a decision. When the SES light comes on , usually a code is set in the computer and the code most of the time will alert you to where the problem lies. The sooner you get it corrected , the better. It doesn't always tell you exactly what part(s) are malfunctioning. You don't have to buy anything, just get the code(s).