Originally Posted by seamsealer
At my last oil change, first one for me with this car, they said it was normal when you put it in drive. I call BS. There should be no difference between neutral and drive.
This is incorrect. There is a difference between the two and its totally understandable. Here is why. When the car is in park for one, the idle general bumps up slightly, usally 150-200rpm higher, this alone smooths out the idle. This comes into 2 and the reason why 1 happens. When you move the Lever to Drive, or D, the load of the engine transfers to the Transmission causing an RPM drop. Why? Because the car is anticipating you to GO. When you hold the car up, by pressing on the brakes, the vacume pressure alone used to use the brakes even can cause an RPM drop ever so slight. So to say there is no difference is not correct. I wish I could explain it better, but its completely normal for Idle to change when going from P to D. What I am talking about, is idle flucuation at idle that makes the car shake a little. I am still learing about this "Smart Alternator" and I do feel it does indeed come on at idle. I don't think its a "fixed" time. When the ECU reads that Voltage drops at any given time the "Smart Alternator" kicks in, regardless if your at idle or not. I am still researching this.
There are many reasons for rough idle: Poor quality gas, outside temp, A/C on or off, Smart Alternator, Faulty Coil Pack, Throtle Body is Carboned up, bad engine or tranny mount, I mean I could go on and on...Most likely though since these cars are new, and the engine is newly redesigned for this new Elantra, it could just be a trait of the car period. All Engines have their "Traits".
So do some work yourself. Keep an eye on your MPG's because that is a good indicator about how well a car runs. If your getting 26mpg's when you usually get 33 that says something. If you step on the gas and it just doesn't take off right, you know? Those are indications of something more serious. Sorry if I got off point......