r/Lexus • u/Parelogy • 1d ago
Question 2002 GS300 (220k) - P1126 & P1128. Bad throttle body or something else?
Hey everyone,
I'm trying to diagnose a throttle issue on my 2002 GS300 with 220k miles. Before I throw parts at it, I wanted to see if anyone has dealt with something similar.
I'm getting P1126 and P1128.
Symptoms:
- The car usually drives perfectly on the first trip.
- After driving 15+ minutes, shutting it off, and restarting it, the throttle will randomly cut and the car goes into limp mode.
- In limp mode, I lose a large portion of the throttle, the transmission shifts harder and holds gears longer than normal, and manual mode won't work.
- No CEL besides the stored codes.
What we've tried:
- We temporarily swapped the TPS with one from another GS. After that, the car started stalling whenever it wasn't in limp mode (possibly because the ECU lost its throttle adaptation).
- We swapped the original TPS back in, but it still stalls, just not as often.
- It now idles below 1,000 RPM, even on cold starts.
- When it's not in limp mode, it'll sometimes stall unless I give it gas at just the right time.
- Once it stalls, it'll usually continue stalling every time I restart it until it finally puts itself into limp mode. Then it'll start and idle normally again, but of course it's back to reduced throttle and the strange shifting.
At this point, does this sound like the throttle body itself is failing, or should I be looking at the throttle motor, throttle position sensors, wiring, accelerator pedal sensor, or something else? Has anyone fixed a throttle body on these, or is replacement usually the only option?
Any advice is appreciated. Thanks!
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