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I recently began having problems with my Sentra. It started to stall in heavy traffic and red lights. The dealer has replaced the EGR valve, Crank sensor, and the computer box housing. The car is no longer stalling but the RPM idling is starting to have an issue. When at a full stop the RPM gauge idles about 800 rpm but then all of the sudden it drops to less then 500 rpm but regains its rpm. I can not figure out why the car is doing that nor can the dealer. When they check the car it always comes up good and never does the problem in front of them. I would greatly appreciate your opinion on this.

When all areas check out good, then the basics need to be re-examined! You did not let me know how many miles the car has so I am going to assume that this 2 year old car has around 30,000 miles. If it has this many miles I would make sure the Mass Air Flow sensor is clean! Air filters don't get changed as often as they should and dirt and pieces of the air filter contaminate the Mass Air Flow Sensor. This can be cleaned with an aerosol can of electronic contact cleaner (non-lubricated type.) If cleaning of the MAF does not help, then clean the throttle body as well as the Idle Speed Control motor. This is something that needs to be done every 15 to 18,000 miles. They get sticky and "coked" up over a period of time and may not respond fast enough when you come to a stop. And this may be causing the erratic idle that you are describing.

 

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