How should the engine sound. How quiet should it be. I can only hear the main fan belt and the big fan noise which comes on and goes off. There is absolutely no vibration but the sound insulation is also dam good. Running with the hood open what should be heard and how loud should it be. Thinking of going to a Lexus dealer and checking a low mileage model. Any advice.

GS300's should be very quiet like LS400's, not on the noisy side like IS200's.

With the bonnet up it might sound very slightly rattly/tappy but only slightly, it just seems to be a nature with all Toyota VVT-i engines for some reason.

Toyota always recommended buying new with high-mileage than old with low-mileage, so get the newest you can afford as mileage is totally irrelevant to these, we bought our LS400 from a Lexus dealer with 136,000 on it and it's absolutely superb, and i've been in one that had done 320,000 and to try it you'd think it had only done the 20,000 miles.

Well. Thanks for that. But briefly in little more detail. A few months ago it was very quiet. I have now noticed that the revs are a little high. Could this be the cause? Before the rev counter needle was on effectively 0. Now it’s between 0 and 1 at idle. I very much suspect that is why there is extra noise. What could have caused this? At idle should the needle be at 0 when in Park. During this time nothing was serviced. Is it my imagination. Can the idle be adjusted if so how and where should the needle point? I think its suddenly raced dont'know how. The sound level is definitely higher than before.

GS300 Performance Data: Could not find Idle Setting:

http://www.autosite.com/new/grabbag/perform/3346.asp

The idle speed should be about 750rpm with the air con off. If the air con is on then it will raise it a little.

You cannot adjust the idle speed. If it is incorrect there are a problem somewhere.

OK. Well I think it’s as quiet as before again its all in my mind. In N the revs are slightly raised as is the same case when in P. I would agree with 750. When on the brakes the revs drop making the sound less. I would also reckon the sound level is affected by how hot, cold, warm the engine is during, after short or long drive. But there are a lot of electronics in the car to control the engine and transmission.

Yes if the car is in D then the revs will go down to around 600rpm due to the next load on the engine.