Idle Rev When Aircon Off

[qha_vn]

my 1990 LS400 has perfect idle rev whenever aircon is on (650rpm steadily) but when aircon goes off, rev goes down to 550 and below causing unpleasant vibration

is there an issue? and how can i rev it up to factory recommendation 650

thanks

[qha_vn]

Hi qha_vn,

most likely one of the idle speed level of the Idle Air Control Valve has problem, try this sort of maintenance and see if you can fix: http://planetsoarer.com/IAC/iac.htm

hope this helps