Unsober1

The thing I find strange is, why is the hesitation so random ? A year apart ?? If it truly is the engine, heads, or its parts, then why doesn't this condition occur more often ?

Devh

I read an interesting article about ten years ago about fuel quality from the branded gas stations and the cheap stuff. Most people would be surprised to know that all of the gas that comes to your local region is from the same distributor. The major oil companies divide up the regions and standardize their gas to be the same except for where one region will have more or less ethanol.
Basically you get the same gas but the only difference is what ever extra additive the brand station adds at the pump. What the article also mentioned is that busy gas stations had better fuel quality because the filters were serviced more often.

I think there is value in branded gas because of the extra additives they add at the pump. Toyota published a white paper on fuel quality stating there was not enough detergent in regular gas.

Devh

I cant agree more. As long as it's not personal debate is the best way to bring forth good knowledge and to be able to scrutinize ones claims for the benefit of discussion.

Devh

I would have kept my mouth shut about the VVT actuators if it wasn't for an epidemic of people reporting the same thing after an oil change. It's certainly not coincidental or psychological. There is something with new fresh oil that is related. I don't see how we can tie this into the valve guide wear to make it work. I don't see how we can tie in valve guide wear in the absence of oil consumption. Random hesitation conditions have been reported with VVT issues not just with Toyota but Honda as well.

Trumpanche

Used my new engine data logger (BlueDriver) to monitor the engine on a trip similar to the "special" route that seems to cause the hesitation. It was evening and 86 deg F (as opposed to typical drive home in 95 deg F), but I couldn't get the car to stumble this evening. I could see that the throttle, MAF, oxygen sensors, and ignition advance all seemed to be behaving as expected. The long term fuel trims stayed quite steady the whole trip (~40 minutes). One bank is a couple percent different than the other, but we're talking -1.6% and -3.1%, so nothing that screams 'look at me!'.

The ONLY thing of interest was that the BlueDriver checks the codes in the various computer modules throughout the car, and one code that was set seems 'suspicious' (here I go being optimistic again). The codes that came up are:

----Antilock Brake System Codes Scan Report----
2 Antilock Brake System Trouble Codes:
1. C1241 Low or High Power Supply Voltage
2. C1300 Skid Control ECU Malfunction
The skid control ECU outputs this DTC if malfunctions are found in the circuit inside the ECU by self diagnosis.
Solution: Replace the Skid Control ECU
NOTE: When replacing the skid control ECU, perform initialization of linear solenoid valve and calibration. See: Brakes and Traction Control\Antilock Brakes / Traction Control Systems\Testing and Inspection\Programming and Relearning\Initialization

The C1300 code made me wonder. If the car is skidding, the controller pulls power from the engine, right? Any chance there's a false trip of 'skidding' under certain conditions (some guys on here repeatedly mention right turns)? Still grasping at thin air, right? I would be interested to know if this code pops up for anyone else.

Devh

That's very interesting. I would clear the codes and start fresh just to make sure.
Keep an eye out for voltage fluctuations. Also keep an eye out for any unusual brief spikes in the sensor data.

Unsober1

Devh, you continue to bring up valid points that I do agree with. However, you stated that this information was about 10 years ago. Above I listed 3 possible fuel issues. One of them was the use of ethanol. Years ago, ethanol wasn't as wide spread to nearly all gas station as it is now. Most all has 10%, and I dare say more ? I have seem gas stations that carry e-15 (15% ethanol). I know even less about ethanol. And I have tried seeing a difference between pure gas and one with ethanol. I have a few stations locally that sell both. I personally can not tell a real difference. Usually I share the car with my wife and rarely run the entire tank out myself. I truly believe that this shouldn't matter, but I am looking at what variables could cause this

Doublebase

Well honestly...a couple things...one, if the TSB describes all of our hesitation issues, then the car is basically junk and we all need to sell them and join a Honda forum. And two, why would a knock sensor act differently to detonation or preignition, then to a valve rattling ever so slightly in its bore? They're both noise - noise that would be picked up by a knock sensor.

The thing with TSB's is there are literally hundreds of them for every car on the road, yet only a very small percentage of the TSB's will affect your car...some more than others, but a lot of them won't.

These cars don't exhibit worn valve guide symptoms, they don't burn oil, misfire, smoke, make noise, or lose their smoothness or power as they age. At least mine hasn't, yet I do get the hesitation a couple of times a month. I'm out of warranty (as many of us are), so walking into a dealer and telling them, yeah just slap two new heads on my car, is not an option. Not when it'll cost you 9-12k dollars to fix. So I'm going to keep driving it...keep doing my maintenance, keep putting the right type of fuel in it and hopefully continue to put my 30k trouble free miles of driving on my car every year.

And if it is the valve guides? I'll be trading it in for a Toyota Avalon

Lextrician

I agree with the possibility with the skid control or let's say traction control because with my hesitation it is during turns, it also happens more commonly with a certain brand of gas that I no longer use. It can be a coincident but mimes is hit or miss normally my car runs like a top but it almost feels like the tranny is searching for gears as well.

Devh

I can tell you that I have no love for ethanol. It pretty much ruined a lot of my yard equipment which I had to spend the better part of the day replacing primer bulbs and fuel lines because of it.
I also don't like the politics behind ethanol either not to mention the performance drawbacks however our cars were built around the fuel type that we use. Modern cars and newer lawn equipment is built around this standard and has been mostly trouble free. Some of the flex fuel cars can run pure ethanol and it is something that turbo enthusiast crave to get the most boost.
I can see a bad tank of gas being an issue that could cause hesitation but it would be pretty obvious for that period of time.

7milesout

While it is true that it's possible the valves could create a condition the knock sensor would detect, as you state ... there are plenty of other ways to engage the knock sensor. Like detonation. And this fuel discussion is intriging.

Here is as far as my brain has gotten. I generally find myself a very good problem solver. But dagum if this problem isn't baffling.

• Oil viscosity - I don't believe it is related to this. Other viscosities are going to protect, but would very slightly affect mpg.

• VVT system clogging - I don't believe it is related to this. If it were, I believe the issue wouldn't come and go. It would come and stay, and then be taken for repair.

• Valve guide wear - I don't believe it is related to this. There are no other related symptoms going on. This problem would be accompanied by tell-tale signs.

• Detonation from fuel problems - maybe. But it doesn't explain the hesitation immediately following an oil change. But at 45 mph, my car is turning 1,250 - 1,300 rpm. Fuel burns so rapidly, that this low of an rpm is detonation city, if every engine system is not working well and/or if the fuel is of a low enough octane. The performance guys like ethanol because it has a very high octane rating. So they can increase their compression ratios without inducing detonation due to the ethanol, resulting in more power.

I also want to add right here that due to the addition of ethanol, and it having a higher octane rating than gasoline, that "gas" with ethanol is reformulated. Meaning, when forumulating gas and ethanol to achieve a 91 octane rating, the gas that is used is LESS than 91 octane and the ethanol having a higher octane is mixed with it to achieve a rating of 91. Do I think this can ever be screwed up? Sure. But even more than that, ethanol tends to settle to the bottom of the tank. If the fuel take is from the bottom of the tank, what happens to the octane rating when a high percentage of the ethanol that *tends to settle to the bottom is used up? And then the fuel being used is more like 95% gas & 5% ethanol? The octane rating would be lower than 91. That being said, I will always run 93 or higher octane (but have never seen more than 94) in the LS. 93 octane is going to lower also, if the ethanol happens to get used quicker, or the formulation is off. But it will always be higher than the "91" ratings under the same conditions. Don't read more into this. I'm not saying ethanol is ONLY at the bottom. It tends to settle to the bottom. But driving the car mixes it up. But I tend to believe if it has sat for a while, the greater percentage of ethanol will be at the bottom. Just a theory of mine ... I've been wrong before (i.e. I'm married).

• Oil change related - Yes. I believe it is related to this. But not in the ways that have been discussed. Not because oil drains out of some component. Because cars sit all night long, and frequently days at a time. Oil is draining out of the same components during that time as it does during an oil change. There's something else ... but darned if I know what it is. Could the oil fill neck be pouring the oil down own to something that could be getting temporarily "saturated?" Could the oil filter elements for the fact that they do not get pre-filled / pre-lubed cause some delay in oil delivery? It seems these last 2 questions may have some merit. But in either case I think these would be a non-issue with 10 seconds to 2 minutes of the engine running. Not a few hundred miles. Who knows?

I have a Japanese friend who still works in design with Toyota. Unfortunately he has not responded to my emails. It's been a long time. But I was going to see if he would put me in touch with the engine guys. I'm betting they know this issue. I just can't seem to get this guy to respond to me ... makes me wonder if I am using the correct email address.

Lexuslsguy

You guys might find this interesting. I called and spoke to John at CarSpec from the article. We spoke about the common issue and he did recognize that many seem to experience the problem after an oil change. He also did not think the oil control valve was the culprit as he has replaced quite a few and the screens were rarely dirty.

He actually said the issue is not very common and that Lexus has updated the head multiple times. In 2009 and 2012 I believe. The cost to replace the heads is about 10k dollars. Apparently you can buy the parts to replace the guides and valves but Toyota / Lexus says you should not repair the heads but replace.

He also mentioned the proper way to determine if the valve guides are causing the problem is by a compression and leak down test. In some cases you can actually remove the the valve cover and wiggle the valve itself. Anyway, it was very interesting to speak with them. He was pretty confident that the knock sensors pulling extreme amounts of timing is the root cause. Whether the valve guides are alway at fault I guess is debatable. He stressed a resonance happening in the head engaging the knock sensors and causing the car to fall on its face as he describes it.

Devh

I agree with the mechanics comments but he did not come to any conclusions why the condition occurs after an oil change only that he acknowledges it.

Well this is interesting revelation if there are in fact screens. I believe we as a community looked at various diagrams where the actuators go and found no evidence of the screens that are found in other Toyota engines.
One of you guys needs to find the location of the screens.

Doublebase

Thanks for the information, I will say that I have some questions about his remarks.
1. He said it's not very common
2. A leak down and compression test wouldn't show a worn guide. The valve sits on its seat during a leak down test...it will seal that cylinder unless it's burned. The .010 of an inch in wear that this guy measured would not cause that valve to sit crooked on its seat, so it would not show anything on a leak down test. As for a compression test? Basically the same thing unless this valve was jumping all over the place, which probably wouldn't even happen if you had worn springs, never mind guides. Again, the valve would have to be burned.
3. In his original picture he was measuring the play in the guide by pulling that valve way way way past where it would travel during regular operation - this would cause some of the play he experienced off that dial indicator.
4. He said many experience it after an oil change, that doesn't lend any logic to a worn valve guide. Unless the oil at that time is too thick and doesn't feed down into the guide, causing it to knock. Highly highly unlikely.
5. Is there any chance that the heads he's replaced come from customers that waited a long time to get the valve spring recall done? I really wonder about that, because I guess it's possible that a weak spring - if left to operate too long - could possibly (and I mean it's a slim chance), could cause the valve to perhaps wear the guide a small small amount.
6. Hey I could be totally wrong.
7. It wouldn't be the first time.
8. Did he mention if the cars showed any signs of worn valve guides? The typical stuff like oil burning, smoke, etc.
9. I'm running out things to add, but I want to make it to ten.
10. I agree that replacing the valve guides is not practical...nor is spending ten grand for heads.

Lexuslsguy

All good questions that I don't have the answer too. It sounds like even Lexus does not fully understand what is going on. He did say that most of the customers who have major work done due to this issue are covered through the dealer and a field engineer (I believe that was the term he used) is involed due to the cost.

He also said it was important to data-log if possible and monitor the knock sensor during the hesitation. Also something difficult to do with how random it can be. He did not know why it seems more prevalent after oil changes. This does seem odd. Maybe it's just a combination of variables to create resonance in the head. I think it should be noted that this problem does not happen to low mileage vehicles. This would clearly indicate to me that some kind of wear or play is involved.