Rhambler

Well, I just read this entire thread. Interesting and seems a mix of two different issues.

And I'm glad I'm not the only one that recommends a good old-fashioned "Italian tuneup," lol. I agree, these cars are so gently driven, for the most part, that heating that engine up might help more than harm. And I say MIGHT, as I'm just speculating, but I'm not the only one based on what others here have said.

Here's another 100% CONJECTURE and SPECULATION on my part: maybe after draining the oil, the oil pressure takes a while to build back up. Even after starting it and letting it run and pressurize, the low viscosity oil takes a while to fully get back to the valves and it's sensing that slap (as mentioned previously in this thread on a similar issue) that could be misinterpreted as a knock and the computer is retarding ignition as a preventative measure. After a while, the oil fully seats and pressurizes around the valves, enough so to reduce the problem.

Also, since it has been reported on turns, maybe the gravity of that turn is exacerbating the problem in one or a certain part of the engine in regards to low oil pressure and subsequent valve noise and the engine going into a misinterpreted safe mode/ignition retarding.

AGAIN, WARNING, I'M JUST CONJECTURING AND SPECULATING, lol. I have no idea really, just theory-crafting as what else could an oil change impact?

johnnyg66

Interesting. When I did my oil change I miss calculated how much oil I needed. I ending only putting in 9 qts. I know it is 9.3 or so on a refill. But the oil that came out was put in last April. It only had less than 1000 miles on it. I measured it out I think it was close to 10 qts that came out.

The dip stick is right at the top notch when I check it now.

Could the amount of oil be a factor in this issue ??

roadfrog

My issue has never returned since doing the Toyota Engine Oil System Cleaner and switching to 0W20 synthetic (TGMO). Nearly two years now and 40k miles. Prior to this, I had it happen on both of the previous oil changes.

Rhambler

Again, I really have no idea. I'm just throwing out wild, hair-brain ideas. Would the amount of oil impact this? No idea, although I don't recommend anything other than what the manufacturer recommends. The theory that I proposed just assumes that after draining, certain parts of the engine become oil-starved. Assuming it's around the valves, the computer is forcing a self-preservation mode upon hearing that knocking.

Why those parts become starved (assuming I'm even right), I have no idea? It could be deposits, which means it might take a while for that new oil to work its way back to the valve guides and springs. Or it just could be the nature of the engine. Next time you change your oil, start the car and let it idle for a few minutes before driving it. Let that fresh oil heat up fully before taking it for a spin.

Again, take what I say with a huge grain of salt. I'm just widely speculating.

johnnyg66

Well it had 0W20 and that's what I put it.

Engine oil cleaner. Have to look into that one.

7milesout

The problem with that theory is that if draining the oil was causing a lack of oil at the valves, this would be the case of every overnight sitting of the car. I bet most on the forums drive their car to the dealer or to a quickie lube type place for an oil change. The engine operates just prior to the oil drain. Then it is drained. How long do they hold the drain open? 5 minutes? Maybe ... if that long. That 5 minutes the oil is draining is not going to drain as much oil off the top of the engine as it sitting overnight.

It's an interesting thought, but I don't think it holds water.

Here's another thought. Could the oil pick-up from the drain pan be getting an air bubble in the line when the oil drains below it during an oil change? I'm not certain what these pick-ups look like but I'm guessing it's routed to "near" the bottom of the oil pan. And if there were a bubble created in the pick-up, could it be that this particular design takes a while to work that bubble out? I'll say that this doesn't sound likely, but just throwing an idea out there. During the time that this "bubble" is in the pick-up line that it doesn't pump oil as efficiently creating a deficit elsewhere in the engine that is leading to this occasional stumble? An oil change, and speculated bubble in the pick-up brings this on? And maybe time reduces the size of or eliminates the "bubble" in the pick-up?

Sounds ridiculous, but hey, nobody has figured this thing out yet so who knows?


7milesout

roadfrog

I do know that DEVH (where is he these days?), speculated that my switching to synthetic oil cleaned up some gunk in the engine and became lodged in the VERY fine screen in the VVT-I system, that eventually disolved. Apparently it's possible that previous service done at the Lexus dealer was done with 5W30 NON SYNTHETIC, during it's first 60 k miles by it's first owner. Synthetic's ultra cleaning properties may have been the initial culprit. I have absolutely NO doubt that this issue is oil related...specifically, oil viscosty and synthetic vs non.

CRowe14

I swear this is such a strange anomaly.
When I purchased my LS, it was from a non-Lexus dealer and they had Lexus change the oil about a month before I bought the car.
Between the time it was services and me purchasing the car there were 18 miles placed on the car, and when I test drove it, there wasn't any hesitation what so ever.
Upon reading about the hesitation issues here-syth versus non-syth and the weights, it prompted me to contact the dealer who performed my oil change and see what they used.
Come to find out they used FS Mobile1 0W20.
Though I didn't have any issues, I had requested at my next oil change, that Toyo FS 0W20 be used. The change was completed and no hesitation.
Now, upon my most recent oil change, which was again performed at a Lexus Dealership who stated that they only use Toyo FS 0W20, once the change was done, I experienced hesitation for about 80 miles and it went away.
I have no clue what to draw from this experience other than (based off of what I've read here) my first oil change amidst ownership perhaps wasn't Toyo FS 0W20 and the change over from what it was to Toyo 0W20 caused hesitation...
I really don't know.

7milesout

My previous oil change went to full synthetic Mobil 1 0W-20. From I don't remember which brand, maybe Castrol GTX 5W-20 (not synthetic).

No hesitation on the 5W-20 non-synthetic, and no hesitation on the synthetic 0W-20.

qpman

Good luck with your hesitation problems. I had a 07 LS with similar problems that became noticeable at 5000 mi and unsafe at 30000 the car was in the shop from Feb to May when it was replaced with an 09 LS. The 09 worked flawlessly until the 75000 mile service at the 90000 mile service it became unsafe but I battled the hesitation problem 9900 more miles, in that time the engine had the upgrades and what ever else it needed because it was still under warranty. At 99500 it sat at the dealership for 3 months. I traded it and said good bye.
PS My cars have had all the service done at the Lexus dealership and only Lexus authorized parts were used including oil and filters.

Rhambler

Just curious but what was the dealership doing with your car for that long? Three months seems like an awfully long time and nothing ever came about from it? Did they ever make a diagnosis?

I think from what I've read is that the hesitation is caused by the engine ignition timing. Now whether it is caused by actual knock or because of noises that sounds like knock due to other issues remains to be seen. So the engine is just going into self-preservation mode, as designed.

1. The car is actually pre-detonating and causing almost imperceptible knock that is picked up by the ECU and the car ignition timing is adjusted and causes hesitation.
2. Oil issues, possibly oil starvation issues (somewhere) might be causing noises in the engine that mimics knocking and again, the ECU car ignition timing goes into self-preservation mode and causes hesitation.
3. Carbon buildup can also cause these issues I think by either causing pre-detonation or through other not-so-pleasant means?

The other hesitation is due to the drive-by-wire nature of the throttle and not really related to this "hesitation" I presume and is more or less driver dependent on how quickly they can throttle up on the gas pedal?

In any case, I wouldn't be happy for the dealership to be sitting on my car for three months without much resolution. Please share what they said?

qpman

I had a loaner for that time and the engineering dept was directing repairs

MyLS460

Follow the Lexus spec for the 07-08 LS: 0W-20; I use Mobile One Synthetic . . . 9.1 quarts (for the noted LS vintage).

snoball

I own a 2008 GS 460. And I am having the acceleration issue as well. I read through this entire thread and there is a lot of "back and forth" about what will actually fix this issue.

roadfrog

Well, you have nothing to lose by doing what I did. I have not had the issue return after two years and nearly 50k miles. To sum up, buy a bottle of Toyota Engine Oil System Cleaner and use as directed. Then fill with TGMO 0W20. If you can't find the Toyota Oil System cleaner in your area, order it online, or as a last resort, use the Rislone product.