I wanted to start a thread specifically about failures within the throttle body concerning the GS300
(1998 in my case)
My symptons were:
VSC, VSC OFF, and ENGINE Lights would come on, followed by my car going into Limp Mode, where only that last 25% (if that) of the throttle would respond (basically have to floor the pedal to even move at all).
During the mornings, or when the engine was COLD, the throttle operated normal...then once the car warmed up, usually at about 10 mins, the problem would start...it happened intermitantly at first...1 or 2 days over the course of a week, then it became more consitent, until last week it became a daily problem.
The first part I tried was the Throttle Position sensor, which is on the front side of the throttle body, and the easiest thing to replace...this didnt help at all. $300 part from Lexus
, $80 part from RockAuto.com (exacly same part toyota OEM)
THE PART THAT FIXED THE PROBLEM:
"Idle Valve Motor", which is the larger electrical object next to the TPS on my 98 GS300. Problem is solved.
The Codes I got were P1120 and P1121 - Accelerator Sensor problem. However it wasnt really the Accelerator Sensor, it was indeed to actual electrical Motor that controls the opening of the Butterfly valve inside the Throttle body.
I found the problem by good old trouble shooting, and using an ohm meter to see if the throttle electric motor was getting elev, I found that the elec motor just to the left of the TPS was basically freaking out and shutting down. The Accelerator Pedal Sensor is on the Back-side of the throttle body where the throttle cable connects to, and has a spring on it. It was fine.
GS300's are indeed "drive by wire" concerning the throttle...the cable triggers the Accel Pedal Sensor, which sends a signal to the ECU, the ECU then sends power to the Idel Valve Elec Motor (next to the TPS), which opens and closes the mechanical butterfly valve, then the TPS sensor detects how far the elec motor is actually opening the butterfly valve...its a closed-loop feed-back system, meaning any failure in any sensor will cause the entire systm to fail.
The throttle cable apparently is ONLY there to allow the fail-safe of having that last 10-25% throttle when the electronic system fails...there is a gearbox inside the throtle body which allows the tail end of the throttle to manually engage the butterfly valve...the rest of the time, the butterfly valve is 100% opened and closed via the idle control motor.