Rough Idle on 1999 rx lexus 300

As a general rule all that is needed for correcting an idle air control valve problem is cleaning the (smallish) air bypass port/channel. Clean the port/channel/orifice, unplug the battery so the engine ECU is forced to "relearn" the PWM setting for the valve's control solenoid, and be on your way.

If you had the spark plugs replaced the shop or person that did this work had to remove the intake and if they did not replace the gasket the vehicle should be taking in air and causing the vehicle to have rough idle.I would take it back to the shop and mention this first i would pay another shop to run full diagnosis and find out if the shop where you had this work done is responsible for not advising you that they needed to replace the intake gaskets.