2002 Ford Other

My 2002 Windstar with 120,000 miles is shaking when the engine is cold. The engine light came on last week and I took it in to the dealership. They told me that two parts are broken in the emissions system (don't know the names of the parts unfortunately). They told me the van was driveable for a while but that I should get these two parts fixed asap. My question is: could the shaking (pretty severe, seems that it may stall but doesn't and then drives fine) be related to the emission parts or are there MORE issues that could be involved? I appreciate your help.
March 7, 2006.

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