2003 Chevy Impala Code P0401

My check engine light came on on my 2003 impala about 3-4 months ago. We had it scanned and code P0401 came up. We changed the egr valve and reset the check engine light. We drove it straight to the gas station which is less than a mile away and filled it up with gas. On the way back home, the check engine light came back on. Sometimes the car is hard to start. I have to try 2 to 3 times before it will start. Any Suggestions???