I have a 2001 Altima with an Auto Tranny and lately I have noticed a erratic idle in when the car is in drive when I am stopped. If I throw the car up to Neutral or park, the idle steadies out perfect. The idle is so erratic when in drive when stopped that it shakes the steering wheel and jumps around 400-600 rpms. Everything else is perfect on the car, good acceleration, and smooth driving. It also gets pretty bad gas mileage if that has anything to do with it. I have replaced the plugs, wires, cap, rotor button, air filter, and the fuel filter. The car has about 33,000 miles on it. Thanks for the help.