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2001 Lexus ES 300 (3.0L, automatic)

The check engine light is on and I scanned it: cylinders 1, 3, and 5 (bank 1) are misfiring. I’m basically getting these 3 symptoms when driving:

1) Cylinders appear to randomly misfire (whether under load or not)

2) Sometimes (apparently randomly) when I brake, the brake pedal doesn’t go all the way down, and I have to press down quite hard to brake properly. It’s almost as if the brake fluid is low, except the pedal doesn’t feel spongey but it feels hard and I can barely press it down. This only happens occasionally, most of the time the brakes are fine.

3) Almost always when driving on the highway it feels like my car would downshift for a second, and then shift back up to the normal gear. Another way to describe it would be like the brakes are pressed down part way for a bit (car suddenly slows) and then released and the car returns to normal. Or another way, as if the car suddenly started driving through honey, and it slowed down a bit, and then returned quickly to normal paved road. It’s kind of hard to describe but I hope you get it.

So far I’ve:

1) Replaced 1 damaged vacuum line (all others looked good)

2) Cleaned the MAF/ IAC valve/ throttle body

3) Replaced all 6 spark plugs

4) It looks like it has a fairly new oil filter (presumably from a repair when I brought it into the shop for something last year)

The symptoms are still present, what could the problem be?

Attila
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3 Answers3

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The VLSS (variable valve timing) shuttle valve is bad on bank one. It is just under the rocker arm cover, but getting to the cover on bank 1 is the problem.

I had the exact same problem on Bank 2 (cylinders 2 4 6 randomly misfiring) and replacing the VLSS valve fixed it!

Hal
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It sounds like you have a severe vacuum leak in the area of bank 1. This may possibly be an intake manifold gasket leak or other bad vacuum lines. This accounts for the misfire and if the engine vacuum is low enough there would not be enough to run the brake power booster. The easy way to check is let the engine idle and using a small propane bottle (like for doing plumbing) induce propane around the intake. If the engine speed increases then it's sucking in the propane somewhere.

vini_i
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I'm going to go out on a limb here. All misfires are occurring on the same side of the engine. I'm wondering if there is an intermittent ground fault to the coils on that side. It would be extremely hard to diagnose, but it would explain the issue. This would only be true if all of the coils on that side shared the same ground and the three on the other side do not. You might be able to get this figured out by running a separate ground from that side, but again, it would be hard to diagnose. I'd suggest your sudden slow down is due to the loss of these three cylinders at speed.

Pᴀᴜʟsᴛᴇʀ2
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