1998 lexus gs300 runs at 2800 rpm at 65 mph

SOURCE: RPM near 3000 on my 1999 Lexus RX300

What is your speed at 3k rpm? What rpm would you estimate was previously 'normal' for highway cruising? If your Lexus is auto trans, it could be two things, it's either not shifting into the highest gear, or it's possibly slipping in gear (although I would think that would cause the rpms to fluctuate, not stay at a steady 3k). If it's a stick shift, again, it could be clutch slippage, but my choice from your description would be not shifting into the highest gear. Bring it up to highway speed slowly, counting how many shifts it makes, I.m guessing it's a 5 speed auto, but I'm not sure about that.

SOURCE: 98 lexus gs300 codes p1120 p1121

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.

SOURCE: WHAT IS CODE P0715 ON A 2001 LEXUS GS300

P0715 Input/Turbine Speed Sensor Circuit Malfunction

It seems that you may have a problem with your sensor on or in your transmission.

SOURCE: how to change spark plug on lexuse gs300 2003

Hi, You need a new Spark Plugs Spark Plug Wrench Socket wrench Extension (At least 2-3 inch) size 10 socket size 12 socket...
First thing you need to do is find out where the spark plug cover is. Once you figure that out there will probably be size 10 or/and 12 bolts honding it down. Take that off and there you will see sensors connecting to each other and holding the spark plug in the cylinders. Unplug all the sensors and pull out the circular plugs holding the spark plugs down. THey might be a little tight and hard to get out so you're going to need to give it a good tug. Once you pull them out MAKE SURE YOU DONT DROP ANYTHING INTO THE CYLINDERS. You can look down into them and see the spark plugs. Get your spark plug wrench, extension, and socket wrench and stick them down in and push so that the spark plug wrench grabs them. Just simply unscrew the plugs, pull them all out, and then put the next ones in, and tighten them down. Just connect all the sensors, and put the cover back on and you're done. Pretty simple.
Take care

SOURCE: lexus gs300 vsc check engine light gas pedal no acceleration

I have a a 99 gs 300, check engine light is on as well as the vsc light. What is that and needs to be to done to fix it.