Question about 1998 Lexus Gs 300

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98 lexus gs300 codes p1120 p1121

I have 98 lexus gs300 the engin and vsc lights are on, codes P1120, P1121. where to find and how to change accelerator positopn sensor?
Thank you in advanse!!!!

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  • 8 more comments 
  • ninakharat Nov 23, 2008

    Sorry!! I ment accelerator pedal position sensor!!!

    I've posted my problem on other sites too. Looks like noboby knows how to fix it.

  • rememberdee Jan 19, 2009

    i have this same problem for the same car....the vsc code came on ...and i couldn't switch the car into gear...please help

  • Anonymous Apr 20, 2009

    i have the same problems

  • Eddie Lenoir May 11, 2010

    are u talken about tha trottle body position sensor

  • Anonymous Mar 12, 2014

    can find the bolts

  • Anonymous Mar 12, 2014

    2006 Lexus gs300 unsolved problems

  • Anonymous Mar 12, 2014

    my lexus gs300 gear indicator is out

  • Anonymous Mar 21, 2014

    What could it be?

  • Anonymous Mar 27, 2014

    p0141 code

  • Anonymous Apr 01, 2014

    turn off vsc light


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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 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 (exacly same part toyota OEM)

"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.

Posted on Jul 08, 2009

  • theinsura448 Dec 22, 2010

    I have the same problem with my 99 Lexus GS 300, I was told by a lexus repair guy, that he will fix it just by replacing the TPS Switch and the Throttle Position Sensor, which is the same thing. But base on your comments which are very helpful you mentioned that what took care of the issue was the Idle Valve Motor....a part that I can not find anywhere, the stuff I'm seeing online associates it with the AC. If you are still out there please let me know by posting the anwere. Thanks.

  • GS Power Apr 16, 2011

    I have 2001 GS300 and code came up p1120 Accelerato pedal positioning sensor circi malfanction. My sister has same GS and I swapped at first sensor and drive around till same thing happen, like after 4 miles driving. So I went further and swapped electric motor that controls throttle flops and drive again about same distance and light came up again. so I replace both units on the throutle and still got same problem. What else can it be? Please post if you got answers?


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Same first I was told several times that it was the catalitic convertor; but was then told accelerator positioning sensor. We were going to repair it at first ourselves but the were told it would not be timed accurately so in Ga I paid $415 to have it repaired; approx $300 just for sensor and I may have burned up the membrane.

Posted on Apr 23, 2009

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I just bought a used throttle body with all the sensors on ebay, took out my old throttle body w/sensors, cleaned up the used one a bit, then put it in and the car runs perfect now, no CELs!

Posted on Aug 29, 2013

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