Trumpanche

All of the engine codes (including Skid Control and three others) self-cleared (I didn't tell the logger to clear them) and I checked them twice today and they haven't popped back up again. Must have cleared on a power cycle. I will definitely check for them again after my next obvious hesitation.

roadfrog

Day 2 of driving today and the hesitation has not returned and the car drives as good as it ever has. To clarify, the day of the hesitation, I shut it down for the day and didn't drive it again until two days after (yesterday) and the hesitation was gone. Same today.

For those that still consider this to be a fuel issue, why would the hesitation only occur IMMEDIATELY after an oil change and then disappear after a few hundred miles and the only re-manifest itself months and 3-6k miles later after another oil change (three times in my case)?

Doublebase

Wait, so you only get this hesitation after an oil change? I thought you said you were 6k miles into your oil interval when it started acting up on you again?

If it's only, and I mean only, happening after an oil change, it has to be some sort of valve that has drained down from the oil change service and for some reason doesn't fill properly afterwards.

7milesout

Doublebase - I don't believe this is a possibility. Allowing the oil to drain out of the pan is doing nothing extra that doesn't happen with an overnight parking of the car. Likely even less. Generally the car is driven just prior to an oil change. It is shut off, for what, maybe an hour or less? An overnight sitting the oil will drain to the pan, it will have emptied the valve you mention, or any other area more than what will happen during an oil drain.

There's something else. My brain keeps defaulting to the knock sensor due to the coming and going of this problem. I have to believe the root cause of the hesitation is due to signal from the knock sensor. But how does a fresh 9.1 to 9.6 quarts of oil relate to that? Dunno. That oil is poured in from the top, and runs across various things. I've only done an oil change once on the car. From my memory the fill cap is on the driver's side valve cover, near the front. What will 9 quarts flow across? Valves, springs, cams, top side of the head, cam chain, cam gears, etc. I'm not certain about all those items, and not certain what else will get oil directly flowed on it.

This line of thinking of mine does not necessarily hold water either, because this hesitation seems to happen sometimes not related to an oil change.

But roadfrog (Chris was it?) - When your hesitation just recently came back ... did you happen to just have added some oil to your engine? Seems you said you were at like 6,000 miles since your last change. Did you check the oil and maybe add some just prior to getting the hesitation again?

caha14

Bingo. My hesitation began after a battery change and a driver change for a day. The hesitation was horrible: unresponsive throttle, delayed downshifts, premature upshifts, etc. The software was updated, and the car was fixed.

I am not trying to oversimplify the problem. This discussion is fascinating, both from the troubleshooting and technical points of view. It is becoming increasingly clear that there can be multiple factors at play, and in many cases, there is most definitely a connection to oil changes, as described extensively by Chris and others on here (and also as described to me by the Diagnostic Specialist at my dealership - again, dating back a few years). However, broadly speaking, the software update doesn't seem to be high on many folks' lists (I do see it's on your list, Chris!), and I believe this is a mistake.

While I do not know what is taking place any better than anyone else in this thread, I continue to strongly advocate for the software update, not just because it worked wonders for me (and has for others), but also because it is a known variable that is remarkably easy to address/rule out. One thing is clear: under this hesitation issue, instead of timing being retarded slightly (as it would be with lower octane fuel, in a controlled manner where there is no more retarding when "knock" stops), it is being retarded "indefinitely" because in the mind of the ECU, knock is not stopping.

I do not subscribe to the theory that the update is a "band aid". As of the time of my update in 2011, I was receiving the 5th version of the software, so Lexus was evidently "tweaking" things quite a bit since the LS460 was introduced, well before the TSIB for hesitation was issued.

If you have a mechanical problem (e.g., with the valve guides), that problem will not go away with the software update (as outlined in the TSIB and confirmed by technicians). If, on the other hand, there is a source of resonance (as outlined earlier in this thread) or some other trigger for the knock sensors (where your cylinder heads do not need replacement), then the software update may work wonders for you.

Take it for what it's worth, but bottom line is that the software update is, in my view, as low-hanging a fruit as there is in the context of solving this problem. The oil-related considerations remain very much a factor and question, but the update could only help this issue OR further isolate it.

7milesout

Caha - I think I pretty much totally agree with you. And the later cars will already have later or latest software updates. Maybe for this reason, along with the fact that my car has low miles, I have yet to experience this hesitation. But I enjoy the pursuit of finding the root cause.

My thinking would be that what is going on with the software updates *could* be Toyota's way of making the knock sensor less sensitive to what it's picking up on, just after an oil change. Making the knock sensor ignore ignore this input. Speculation only, on my part. And the latest software is a good thing, and worth getting the software flashed.

But alas ... the root cause remains veiled! Let the pursuit proceed!


7milesout

roadfrog

The hesitation in the past ONLY happened after oil changes (3 of them) and then disappeared after a few hundred miles or a few days. This is similar to most others who experienced it. This latest episode, for whatever reason, reared it's ugly head for a very short time (less than fifty miles). Yes, I was at the 6k mile mark on this OCI and have not added any oil so far, so the hesitation has no link to adding or topping up my oil.

I too am intrigued by this phenomenon and hope to be among those that narrow down the cause.

I am also confident that Lexus is working on it as I can't imagine them ignoring it. Too much info out there now and there are entries and submissions on your U.S. (NTSB?) websites. This is certainly a safety issue and can't be ignored until someone is killed or injured because of it.

I will definitely get the software update and see what happens. I was hesitant to do so before as I had been successful in fixing the issue - at least until this last one near the end of my OCI. I was afraid of changing the programming and messing with success.

Doublebase

Roadfrog, keep us posted when you get your update.

One question I have is, does this car have an egr valve? I bet it doesn't and NOx is controlled by the vvti system - like many have said, perhaps after an oil change this system is somehow affected, which may allow both the intake and exhaust valves open when they shouldn't be (under acceleration situations). That would cause those symptoms, because I have felt what an egr system fault feels like when it's opening when it's not supposed to. And it does feel like his.

Then again I'm just as clueless to all of this as anyone else, and I'd tend to think that the vvti system would be monitored by a map sensor or O2 reading...or both if we are talking about the control of NOx.

7milesout

NUTS! Foiled again!

Ignoring it? No. Working on it? Doubtful. As a design engineer who participated in warranty issues and subsequent investigations ... or the lack thereof, I can speak to this issue. In order for my answer to seem resonable, you have to understand ... there are not a vast number of engineers who work on the engine. Or any particular area of the vehicle for that matter. It's far fewer than you would imagine. I would have to guess the number of engineers who were truelly involved in the LS 460 engine development ... maybe 4. Others were involved in managing their work, and others in testing, later others with quality groups, etc. But the actual development. Maybe 4 ... directly. When they "handover" this engine to plant engineers, those 4 guys are reassigned to, either the next engine, another vehicle line engine, or could work on production issues regarding this engine.

When problems occur with this engine, it has to reach a certain threshhold before they'll go back to the engineers that are actually smart ... the original development engineers. The downstream engineers just carry a big hammer and duct tape (oh wait ... that's Hyundai - Kia). But for real though, nobody knows these engines like the design engineers. And they're busy on other things, not working on the problems of these "old" engines.

My guess is, it's not likely a real serious effort has been made to root cause this. Dumbing down a knock sensore is not addressing the root cause. But again, i speculate on what the flash does. Those "sustaining" engineers that are involved in the warranty reports log into ClubLexus and read about what we're figuring out. Once we have it figured out, they'll fix the problem and take all the glory!

There are a separate (small) team of engineers who work on advanced technology. They figure out what has merit and how to make it work. Then they trickle that down to the design engineers and they implement those technologies on their program. It really doesn't take that many design engineers. For example, the guy who does the block, he starts with ... the previous block, and changes / tweaks it to what it need to be for the next vehicle. All other parts are done the same way. Automotive engineering is a well planned out and scheduled series of increments to existing parts. That's why it does not take a ton of manpower.

Except for Hyundai - Kia. They use a different technique. They F--- S--- Up from the get go, and then spend the rest of the time making it barely acceptable to meet the delayed launch date. And then the plant follows the motto: Don't be a squealer ... ship it to the dealer! And them's the facts mates. Be glad to own a Toyota product.


7milesout

CARspec

Thought I'd chime in - note I'm not speaking in any official capacity for Lexus.

1) I've worked on a lot of LS460s and the issue is fairly rare, ie. we don't see many people concerned about it. That being said (while the issue is notoriously difficult to check when the techstream is attached), it's very obvious when it does it. That's a bummer, as I love the LS460.

2) When you check for valve guide play for this issue, you remove the cover and pressurize the cylinder. Giving the back of the valve a bit of a wiggle (spring still installed, cams still in, etc.) you get a leak out the intake/exhaust with only a little side pressure. This is a non-official, quick check of valve sealing. Those that have excess guide wear leak with little side pressure. The valves usually show a evidence of burning. Hotrodding trick.

3) I was pulling them out way too far - flush with the valve seal on the back for all photos. This is only to demonstrate one valve's play vs. another's and is not an official specification. Demonstration only. The worst valve had a lot of play and I came up with this as the best way to demonstrate how much more. I lack the machinist's tools to measure the tiny extra clearance and went this way to demonstrate it. The heads in the photos were from a dealership repair that didn't get sent back for warranty that the shop got because I'm curious. We also used them to develop our walnut shell blasting process for the IS250/GS300.

4) This puzzles me too - I have no idea why it would pop up after an only change, only that it does more frequently. If you figure that one out I'll buy you a cup of coffee - I'd like to know the answer too.

5) We've yet to do any of the heads in the shop (we're only 11 months old!). I refer the guests to the dealership first. If you can get it fixed under warranty (or goodwilled!), awesome. I also have yet to meet an LS460 owner who wants to spend that much money on their car when that amount is a decent down payment on a new one.

6) Me too!

7) Happens all the time!

8) Rolling misfire on one, the other was fouling the same spark plug over and over. Still had a hard time getting the knock sensors to pull timing.

10) You aren't alone.

Lexus has the best customer service in the business. I'd eat my hat if they didn't revise the bulletin or issue another fix for this. I'm sure the field specialists and engineers have something in the works to fix this. Otherwise I'm in the same boat as you guys and look forward to seeing what happens with this issue.

Hope this helps a bit - I'll try to chime in if I run into any others that I see or hear anything through the grapevine. Anyone in Minnesota is welcome to stop the the shop and have a cup of coffee too.

Trumpanche

I had the hesitation occur again today on the drive home. A mix of steady 40-50mph cruising plus sluggish stop and go where you really can't get into the throttle for most of the trip. (basically lots of low RPM high vacuum operation). I felt it a bit towards the end of the 30 minute drive, but then parked the car (turned off) for about 90 minutes (for a good heat soak) and upon driving it again (going into right turn out of the parking lot) I had almost no power. I immediately checked for codes again to make sure it wasn't that Skid Control ECU and there were no codes. Unfortunately, checking the codes kept me from seeing and capturing the live sensor data. Recall that I drove 20 hours to Florida and back with no hesitation, and now I've had three similar hesitation episodes during the same drive home within about a week.

Lexuslsguy

It's interesting speaking about it happening when turning. I have a theory that this is due to gravity. Something is moving in that engine and under the perfect circumstances creates the hesitation.

7milesout

So, the root cause is gravity! Damn! I'm just pulling your leg... I'm beggining to think there are different issues, and these different issues have a side effect of hesitation.

There's

• The Oil Change Hesitation.
• The, "Right Turn Clyde," hesitation. And,
• The Congested Traffic / Low RPM hesitation.

Doublebase

Very thorough explanation, thanks. I understand the leak down aspects of it a little more now, and wow, to be able to move a valve from side to side and get it to move on its seat is surprising (although I'll admit I've never tried that before).
And it's good to hear that the signs were a misfire code on a specific cylinder, because I don't think there are many on here who have experienced anything like that regarding this issue. And I figured you had that valve pulled all the way out to the valve seal, but I understand why you did it now...honestly it's a great idea.

I feel pretty confident that I don't have this issue - thank god - and it sounds like many others don't either. It's a great find by you to have discovered it.

roadfrog

Drove my car LOTS yesterday and without any issue. Stop and go heavy traffic, highway speeds, city, etc.

Today on a short drive, the issue returned but only for a few minutes and a couple of miles (city driving).