Wish I had an answer - sounds very much like a problem I am having with my '92 LS400. I have a parts car, and have changed out the ECM, fuel pump, injectors, fuel pilter, fuel pressure regulator, ran the can with exhaust unbolted (check for clogged CATs, checked out my timing belt for slippage amoung other things, and nothing works. I have no check engine light on. Do you?
My 1991 LS400 just started doing the same thing. Thought it was the mass air flow switch but it wasn't, also the trac sensor was switched, wasn't it either. Next thing I am checking after doing some research is the ignition coil. The mechanic friend I am working with feels it might be a dead cylinder so the ignition coil might be the cause. Hope this helps you or if you found the issue would appreciate an update for help. Good luck.
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SOURCE: 1993 Lexus Ls400 loss of power at 2500-3000rpm
Check your MAF and MAP sensor. The first 80% of your throttle signal from the TPS works with the O2 sensor to try to keep the air fuel ratio to 14.7 to 1 with the ECM controlling the fuel injector spray time and timing the ignition. After the 80% to WOT the ECM puts the O2 sensor in to an open loop and takes the Reading form the MAF and MAP sensor to run the engine richer so there will not be any Detonation to the engine and burning holes in the valves for running too lean. That is why it always feel like you get a little more when you ease off on the gas peddle from WOT. Recap check the TPS, MAF,and MAP sensor and wires to those sensors, if you can get the car scanned that would be great and you may find out which sensor may have gone bad, the other thing to is the fuel pressure regulator may be going bad and at WOT the pressure may be to high causing it to run to rich causing the loss of power. Good luck and hope this helps.
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