Their is no definate answer other than it being a component malfunction in the engine management system. There are far too many devices on the engines available for your vehicle that can cause the symptoms you describe. Stuck EGR, leaking EGR. EGR relay, or breach to the vacuum lines to it. That is just one influential component. There are plenty more that may apply...Idle speed controllers, air bypass valves, mass airflow sensors, manifold absolute pressure sensors throttle position sensors, oxygen sensors, some evaporative control system components.. All these just to name a few will cause these symptoms
But wait and do not dispair! Along with hesitant idle, you also provided a very important fact. Your "check engine " lamp is illuminated. This is a good thing! Why? because it will help pinpoint the problem to the technician that will service your vehicle, You see, before vehicles had onboard diagnostics to relay information to the technician, it was much more of a puzzle to figure out. That puzzle could sometimes cause unnessessary repairs to certain items to "rule them out" This resulted in repairs back then that had big bills from long parts lists where much of it never even needed to be replaced in the first place.
No more of that! Nobody like trial and error repair. It kills the owners wallet and makes the technician look stupid.
That check engine light will lead the technician very close if not right to the problem itself because that is exactly what it's purpose is.
Take your vehicle to a reputable repair facility and they will give you an accurate quote and description of the problem in a matter of minutes.
Some will even read the trouble codes for you for free,(based on repairing it there usually). For the do it yourself person you can get a code scanner to read the code if you know automobiles
Chances are that the problem will at least not be a very serious one.
