What could problem be when entire car shakes upon starting? on 2001 Nissan Altima

check engine light flashes, shaking comes and goes, light goes on and off, entire care rumbles/shakes.

Asked by for the 2001 Nissan Altima
It is a sign of what is mostly a misfire (loss of fuel intermittently) or more likely an ignition coil that is failing. 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.
thank you. I have had issues with misfire before. Dealer would only replace affected part and not others, I am assuming to get more labor from me at a later time. I appreciate your response.