Diagnosis

Too much EGR flow at idle, cruise, or cold operation may cause any of the following conditions to occur:
^ Engine stalls after cold start
^ Engine stalls during closed throttle conditions
^ Vehicle surges during cruise
^ Rough idle
^ DTC P0300, misfire detected

Too little or no EGR flow may allow combustion temperatures to get too high. This could cause the following symptoms:
^ Spark knock (detonation)
^ Engine overheating
^ Emission test failure
^ DTC P0401
^ Poor fuel economy