Engine Performance problem
1999 Ford Taurus V8 Front Wheel Drive Automatic

Engine code PO401 Exhaust gas recirculation flow insuffient detected is this the egr valve or the Dpfe feed back sensor I heard that this can give you a bad egr valve code also?. The car runs fine sometimes and other times misses at low speeds around 1000 to 1100 rpm and sometimes at idle maybe a diiference of 100rpm +/-. I have replaced the iac valve and the iat sensor. At highways speeds or anything around and above 2000rpm the car runs fine. Thanks for your time..