I can't at all explain why this happened, but my 11 Lexus GS350 warped front rotors and all I ever do is keep the car in gear and use the engine to slow down. There is even a Standard Simulation mode that allows me to downshift. I've used this method to nearly completely stop the car while driving around town. I only hit the brakes if there is a car directly behind me that needs to see brake lights to avoid slamming into me. Even then, I use downshift method to slow down. Not sure how this works as it is an Automatic, but seems downshifting does in fact allow the engine to mimic a manual transmission. It is a pretty cool feature that most cars seem to have these days. I use my A/C almost exclusively, so I'm doubting fuel efficiency is at all increased when doing this slow-down method. Most modern cars can idle for over an hour on a gallon of gas, so saving a sip of fuel just doesn't amount to much. Saving fuel on a freeway is the true question to ask. Another one is how in h3ll did my rotors warp?!

Most modern fuel-injected cars can idle for over an hour on a gallon of gas, so saving a sip of fuel just doesn't amount to much. When you use your engine to decline down a hill, your ECU recognizes that the engine is operating at an RPM higher than idle, so fuel feed is nearly cut off at the injectors - some automatics completely shut off fuel until RPM drops closer to required idle speed. In a manual transmission car, I'm not sure how the fuel delivery system is handled. In my own cars, I rarely use brakes on a downhill - engaged gears take care of that issue and both of them have "Manual Trans Simulation Mode" which allows the Auto to act like a manual. Pretty cool feature that does in fact slow the car to a near stop in almost all situations. This is how I slow down when leaving the interstate or even going downhill to maintain a certain speed best I can.