The manual well say that because the manual was made when the engine was new. Each engine is going to wear differently and if yours can idle at 800 then your engine is in good shape but his is at 500RPM and I never advised him to make it 1150 I just told him to move it until he's reached the RPM he wants! I want mine at 1150RPM. (better sound at lights) 1150RPM isnt bad its still within specs. It just depends on what he wants. If its sputtering at 500 and thats what his car runs at then he should increase it till its in a better location. I cant imagine his car has anything wrong with it.