The egr valve on my grandmothers cavalier keeps getting stopped up with carbon. What causes this? It has less than 30,000 miles.

 

usually from driving the car like an old granny! hehe...sorry, On such a low mileage engine, the main culprit would be from not driving it hard enought. Lemme guess, she never takes it out of the city, goes to get groceries, and goes to church then back home?

 

yep that sounds like how and where she drives it.