I have been away for a week and no one has touched my car. When I got home I turned on the car and it shook for about 20 seconds, then ran normally. I drove to work. When I left work and turned the car on it began to shake again for about 20 seconds then began to run normally but the "check engine soon" light came on.
My car shakes when I turn it on on 2005 Nissan Sentra
Moisture may have gotten into the ignition system while the car has sat causing a misfire on start up or worse could rodents have done damage to engine wiring (see it a lot during winter). If the Check Engine light/Service Engine Soon light illuminates while you are driving, the car's on board computer sees a fault in the engines management system that is causing an excess amount of pollutants to be emitted from your car. This could result in engine damage if left neglected. Some problems that can cause the Check Engine light to stay on may take two "drive cycles' to complete before illuminating the Check Engine Light. The computer sees a problem and looks for an identical set of circumstances to occur to confirm that it has indeed seen a problem before turning on the light. A Check Engine light that continually flashes while you are driving is serious and is a sign that the computer sees a problem that seriously risks damaging the catalytic converter which may result in an expensive repair or even may cause a fire! Diagnostic codes are stored in the vehicle's computer and can be retrieved using a scantool that communicates with the computer in your car. We have in our Repairpal website an encyclopedia with in depth articles about computer, and computer control systems, emission and driveability problems. http://repairpal.com/check-engine-light