Loving my 2010 RX450, still trying to get used to the differences from previous cars. For example, today my wife was driving and we were stopped in traffic on a slight downhill offramp. It felt as if the car were idling very roughly but what really seemed to be happening was that the gas engine kept starting and stopping. Any way to avoid this?

 

I have 2010 toyota prius and lexus RX 450h. They do the same thing as yours. For hybrid cars, They stop the engine frequently to save fuel, especially at full stop. Sometimes they need to run the engine to charge the battery no matter empty or nearly full battery. ( I don't know reasons behind this).

For roughly feel while car was idling, I think, because the hybrid car was super quiet while the engine didn't kick in but when the engine start to kick in, you can notice it very obviously and feel a little bit roughly. I bet if you drive RX 350 which the engine run all the time you will just get used to it and it will quiet in its own way.

P.S. Sorry for my English, it wasn't my first language.

 

Jellopy hit the nail on the head - the rough idle is a result of the gas engine charging the battery - this rough idle occurs when the battery is depleted and coasting/stopping isn't regenerating enough power to charge it.

 

Try charging battery and reverse at the same time, that's really rough. Usually at work, I have to climb 4 floors up to the parking lot in my office building. Once I got there, the battery would be low and charging, when I backup into my spot, I can feel and hear the roughness.

 

Do you guys feel a jerk when coming to a complete stop? It almost feels like a tug just before the stop.

 

That may be where the actual brakes are being activated to finish stopping the car. Until I think 10mph it uses the traction motors to recharge the battery while you slow down.

 

Okay just making sure haha. Thanks!

 

The rough idle is due to the engine running at much higher speed to recharge the battery then the usual 650-750 rpm idle of typical cars. The older RX400h that I used to own will drain the battery to a certain point and start the engine on slow idle, which usually last a long time unless I drive the car up to speed. This was not very efficient if you were stuck in traffic jam for long periods of time. With the RX450h Lexus changed the design and now idle much faster to quickly recharge the battey so it can shut down the engine again in a couple of minutes. Together with other improvements like much faster winter engine warm up, I am getting about 20% better fuel economy in my new car. I guess the rougher and louder idle was one of the compromises to achieve better efficiency.