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Power Loss


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I have a 1990 LS400 that I have owned since it was new.

This car always runs well when the engine is cold and also runs well for the first hour or so.

Then the engine looses all power intermittantly but does not die. The car slows to about 15 MPH even when the accelerator is fully depressed. After about 10 seconds the engine goes back to normal for about another 10 seconds. Then the problem re-occurs continually until I let the car rest overnight.

The engine diagnostic light had been displaying for about 6 months but the the car ran fine.

After the power problem developed months later, I checked the diagnostic code which indicated that the right oxygen sensor was bad. I replaced this oxygen sensor with a new one and cleared the diagnostic memory. The engine diagnostic light no longer recognizes a problem and stays off.

I have changed all spark plugs and the spark plug wires.

I have replaced both coils.

I have removed both ignitor modules for testing but Advance Auto, NAPA, Autozone don''t have the connectors to test these modules, although they can test most other cars. I live too far from Lexus or Toyota dealer to make it to them. They want to test the ignitors on the car.

I have checked hoses for vacuum leaks but found nothing.

I replaced the fuel filter and air filter.

I have gone through several tanks of gas so it''s not water in the fuel.

I have replaced the throttle position sensor and this did not solve the problem.

Any help on solving this problem is greatly appreciated.


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Hello and welcome! Wow, I wish I could have owned a LS new in 1990, but I was just starting high school and it was out of my budget. :P

I bet when brand new, these were truely "sweet" cars!

There are alot of guys/gals here with alot of experience under the belt with these cars and surely someone will point you in the right direction.

BIGSTE may have you on the right track.

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