I have a 2004 LS430 with 53,000 miles on it. I have the oil changed regularly between each 3,000 to 4,000 miles. As soon as any problem arises I have it taken care of right away. I have never done the Lexus suggested 50,000 mile service because the engine is fine and I don't feel I have to. When I first purchased the car in 2007 with 13,000 miles on it and for years after that ( how many years I don't know) the engine Idle was so quiet I didn't know if the engine was working or not. That was luxury to me. Now you can plainly hear the idle. There is no doubt the engine is working. There is nothing wrong with the idle. It's not too loud ,choppy or anything irregular .other than you can distinctly hear the engine. I use regular gas these days with no problem. I think when I first bought the car I used to switch sometimes regular and sometimes the middle grade. I questioned the Lexus service Rep. on this question and he said there is nothing you can do the car automatically adjusts the idle and that there is nothing wrong with your car and your idle. There has got to be more to this than that. Does anyone know what I can do to Quiet my engine Idle. Thanks for your help.

What kind of noise? Are you hearing exhaust noise like an exhaust leak or hole in the muffler, a clicking sound like the lifters or fuel injectors, a squeaking serpentine belt, or what?

So do you have an exhaust leak? Or maybe you need new weather stripping, can you go into more depth than the idle is to loud.

Apply some Shin Etsu on all the rubber weather stripping will help with reducing wind noise, road noise, and engine noise.

Are you saying it idles faster or at a higher RPM now?

Could that be MAF (Mass Airflow Sensor) or a dirty/clogged PCV valve?

Verify air filter is clean. Remove the two screw and clean the MAF. There is spray cleaner for this. Do not touch the element.

One thing I've noticed between my 2 cars, is that the 2001 is slightly louder at idle than the 2005. The 2001 has just under 180,000 miles and my 2005 is sitting at 56,000 miles. With mine, it almost seems like the noise is coming through the vent system. Perhaps the foam seal on the Air Inlet Servomotor is starting to fail, causing the noise to be transmitted to the cabin?

Long shot I know...

First thing i would not be putting using regular unleaded like his first post.

Absolutely!!!! Regular? 87 Octane? Yikes. If high test wasn't available I would not drive my car until it was.

Sorry op, its hard to decode this... Are you saying the idle is too high?

If it were you would have issues at the traffic light creeping ahead without a lot brake applied.

If it is just louder, have you looked under the hood? Are all of the OEM sheilds still in place? Have you had exhaust work done where the replaced or removed components?

Absolutely will not hurt a thing unless car is driven hard under a load, or weather is extremely hot.

Just cruising around? No problem.

Yah I agree the ecu can compensate 10%-20% for added or taken away power due to gas octane rating, spark plug wear, etc, the low grade gas would only be a problem when you did aggressive driving as you said above I always put 93 in my car but I also like to get on my car.

The situation is this. From when this car was new and for years after the engine idle was so quiet you did not know if the car was running or not. Now you know when its running. No problems with the idle. Lexus says its fine. But my question is; is it possible to get the idle back to it's original quiet state. As for the regular gas I felt No difference between the regular and the mid grade. I also asked my Lexus Rep. what grade gas I should use. He said that the engine would work just fine with regular gas. The car engine drives as smooth as can be with regular. I guess I'm going more for perfection than there being some sort of real problem with the engine or the idle. Thanks for your input. When I talk about not being able to hear the idle I mean from standing Outside near the car. That's how quiet it was

Yah but how is the idle different is there an exhaust noise or something we need you to specify how the idle is different.

The Idle is different now because you can now hear that the engine is running and before you could not inside or outside the car. Things just changed. Lexus tells me don't worry about it the engine and the idle is fine , No damages but I know the difference and am interested in changing it if I possible can. ?

Check your pulleys, belt tensioner etc.