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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?

  • Do you have access to a reader that can give you information on fuel trims? Preferably with measurement readouts for things like MAF, O2 sensor voltages. Does the lack of brake feel exist after replacing the vacuum line? Any idea which vacuum line you replaced? I like the level of information you've provided so far btw – Zaid Jun 9 '15 at 17:57
  • Thanks for the responses @Zaid the line I replaced was the vacuum line from the brake booster. It didn't fix the braking problem. I use the ElmScan 5 Compact tool with OBDwiz and it gave me the following codes: i.imgur.com/unLXx5C.jpg It gave me this data for the oxygen sensors (not sure what to make of it): i.imgur.com/dXanNPk.jpg and i.imgur.com/0RIA3ra.jpg Paulster2: Yes that would explain the sudden slow down. What you suggest does seem kind of hard to diagnose but perhaps I'll give it a try after a bit more research to see how everything is wired – Attila Jun 10 '15 at 21:43
  • Twinbird, any updates? – Zaid Aug 6 '15 at 9:44
  • I apologize for being away for such a long time without providing feedback. I gave the car away (to someone who knows of it's issues) and no longer have it with me. I bought a new car. I got busy with school and work and had no time to work on the Lexus. It appears the cause of this problem will forever remain a mystery, sorry everyone. – Attila Jan 20 '16 at 7:13
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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!

  • @Attila This is the most likely answer. The p1349 is the giveaway. – Ben Feb 19 '17 at 8:15
  • Thanks for the answers! Unfortunately, the car hasn't been with me for about a year now. I have a new Nissan Micra :) – Attila Feb 22 '17 at 3:39
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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.

  • This sounds very plausible! I've been very busy with work and haven't had time to work on my car recently (hence my lack of activity on this thread, sorry guys). I will definitely try what you suggest sometime this week and post back here. I bought a new Nissan Micra so unfortunately if the check doesn't provide any results then we will most likely never know what is wrong with this car. – Attila Aug 31 '15 at 2:47
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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.

  • If there were a ground issue you'd expect to see p0351/3/5. If the ECM doesn't see an IGF return signal from the coil it set's those codes. – Ben Feb 19 '17 at 7:55

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