I have an 06 TL and from time to time when I get in to start the car. The car would start off dead, then turns on but after it turns on the startup would be a little rough. The Rpms would be at the regular idle rpm range then it would drop like the car is about to turn off then it would go back up again.sometimes if turn the wheel while in park the Rpms would dip then come back up. Even when I drive it, I would hit a red light the Rpms would drop low then come back up. Are my spark plugs going bad? Alternator failing? Bad battery?

 

Have your battery tested at a local automotive store. Replace it if its bad. If its okay, do the idle relearn process: Let the car cool down and then remove the battery for 15 minutes, then connect it and start the car. Leave all accessories off, and let the car idle until the radiator fan cycles on and off at least twice.