P0402, the engine is shaking, 98 ford taurus

Every day when I start the engine, it shakes for a few minites, after some time, the speed of the engine increases suddenly, then the shaking is stoped. Recently the "service engine soon" light is on and show P0402, when I check my car in garage, they said:
1. A piece of carbon wedge might open the egr valve on idle, so the car is stumbled, but if so, the car should be shaking on idle all the time, not the first few minites when I start drive, is it right? should the valve be close on idle?
2. If DPFE sensor cause the problem, there shouldn't be shaking at all, right?

Clean all the ports and the throttle blade in the throtle body and then recheck your codes, dpfe sensor and egr very common failures on FORDS
Carbooned up throttle body can cause rough idle and these codes

How much does the throttle body cleaning cost?
Is it possible that the problem is egr valve? How much does it cost then?

cleanning the throttle body is something you could probaly do your self if you have the tools and the patience, Not sure what they charge for that service, I would think 50-60 dollars at the dealer, I don't know what Ford charges, Where I work we charge 180 dollars canadian and we flush the fuel injectors with a cleaner as well as part of the service. If you're not much of a do it yourselffer then call a few places and tell them your codes and explaint that you'd like to try cleanning the ports and throttle body out first before replacing any parts unless they tell you that it won't fix it w/o replacing something and they'll gurantee their work. DPFE sesnor is very common failure though so you might still need one after the cleanning, not sure what the parts cost?

good luck and keep me postted

Jeff