1998 Lexus gs300 at idle Very loud buzzing type noise from engine

Check this website you find there fuse box diagram for Lexus GS300 (1998 - 2000)

Lexus GS300 1998 2000 fuse box diagram Auto Genius

P0155 O2 Sensor Heater Circuit Malfunction (B2S1)
bank 2 ...side one

either the 02 sensor has failed or getting too much voltage

go with replace 02 sensor first

On this website you find fuse box diagram and description for Lexus GS300 (1998 - 2000)

Lexus GS300 1998 2000 fuse box diagram Auto Genius

Check behind the ash tray.

70% is the ECM PROBLEM FOR THE GS300 2JZGE ENGINE VVTI

WHen you turn on the a/c, the computer kciks up the idle speed to compensate for th load of the compressor on the engine. That tells me your idle air control is not wrking electrically or hte passages are plugged.

On this website you find fuse box diagram and description for Lexus GS300 (1998 - 2000)

Lexus GS300 1998 2000 fuse box diagram Auto Genius

The buzz noise is probably coming from the airflow controls turned off but being stuck in a particular mode such as vents and feet mode or winshield and feet mode, creating a buzzing noise while it is turned off. To stop the buzzing noise turn off the aircondition / heat by pressing the off button, next press the mode button for the fan controls to make the picture point to face only not feet or winshield, this should stop the noise.

Its a Oil Control Valve most likely. Get the valve. Its like 100 from Lexus. Mine did the exact same thing with that code. GS300

The only four rotating items under the hood are
engine
power steering pump
A/C compressor
and smog emission pump.
==== I would check the fluid level on the power steering first. Check for pink fluid leak on the ground,
==== Check the A/C system with the wheel turn to one side and APPLY ALL LOADS.
Example: high beam on,A/C max,radio on and deforster on.
This will give you system a stress test.
All eyes on the pully and locate to part that generate the loud screeching noise.
My bet is on the power steering pump.

Please post more info on the comment window.
I will follow up on it.