I have a 2005 lancer es, the car runs beautiful and doesn't have any rough idle. I have tested every part from the EGR valve - the solenoid and everything listed in the FSM related to the EGR system. All of the parts were tested as per FSM and were fine. The only thing I'm not sure how to test is the MAP sensor. All vacuum lines were cleaned up and are tight. Cleaned the EGR valve....I'm at a loss at this point. Could the map sensor be causing my car to throw the p0401 code with out it having any effect on idle or anything else?