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Tom, ASE Certified Technician
Category: Lexus
Satisfied Customers: 25954
Experience:  ASE Certified Master Technician qualified to work on all makes and models.
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1999 lexus: random misfire..46 mph car starts to buck..idle rough

Resolved Question:

1999 lexus getting misfire on cyl 2 and 4 and random misfire. cyl 2 and 4 were previously replaced (within the last 1.5 yrs) seems to start once car is warm at about 45-46 mph car starts to buck - if i hit the gas it will go away & as soon you decrease speed it will randomly buck. at times it will idle fine and others idle rough. randomly the brakes get hard and feels like you have no brakes. current mechanic feels it is injectors, but i feel it is something else and with the brakes getting hard randomly it is not safe. of course the check engine light is on as well as the trac off even if it is not misfiring; which is temporary.
Submitted: 7 years ago.
Category: Lexus
Expert:  Tom replied 7 years ago.
Have you done a compression test or cylinder leak down test on these cylinders yet or checked the fuel injectors?
Customer: replied 7 years ago.

No. Mechanic wants me to run it with the injector "whatever it is" cleaner I guess; but the thing with the brakes is dangerous and occurs when it feels - one minute normal and the next hard. I don't want to have to take it to Lexus if I don't have to.

Expert:  Tom replied 7 years ago.
Ok so the brake pedal is getting rock hard also and not stopping the car correct?
Customer: replied 7 years ago.

yes. Brakes are real hard kind of like if you were bleeding the brakes. It is periodic. I could be slowing down fine. Then all of a sudden they get hard. It almost seems like the brakes get real hard when the engine idle is worse. The car stops but not not gradually. I have ceramics pads on the car and there is nothing wrong with the brakes. Whatever is wrong with the car is making the brakes hard.


Expert:  Tom replied 7 years ago.
Ok the problem with the brakes is either a vacuum leak at the brake booster or a faulty brake booster itself. The booster is where the brake master cylinder is attached to. The vacuum leak can also cause an engine misfire. As for the fuel injector cleaner you can try that , but I would also check the plugs and the injectors themselves. You might also want to do a top engine service where a chemical is run through the vacuum line of the intake and cleans out all excess carbon from the motor.If there still an issue perform a cylinder leak down test and compression test to make sure there is no engine or valve damage to these cylinders. This is the next step.
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