idle speed 1hz non-turbo

Hi all

Just had my 105 series manual in at the local mechanics today to get the valves checked and a general check over (just bought the car), it currently idles at 900-950 revs when warm a/c off and assume this is a bit high (shouldn't it be around 650rpms? did ask him that but he thought that it's a bit low being a larger diesel??-who am l to argue with a professional?), anyway he thought it is fine, l'm just after a second opinion before l call them again to query it, also they mentioned it didn't need the valves checked as the motor sounded ok, it this right or does one have to visually inspect the valve clearances-have no idea when they were done last-car has done 268 000kms and sounds ok. I have an old bmw boxer motorbike and going by the sound is usually ok (i do adjust these valves myself every 8000kms -very easy to do)- but you do need to aquire an ear for it-so to speak. Just not sure about diesels though as it's my first one.

thanks, Nick