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Hi gang,

Here is a mystery for you all to sink your teeth into....

Symptom: Random shuddering and reduction in power at >85-90km/h.

This happened on the freeway all of a sudden a few weeks ago one late evening. I instantly thought I had a flat tyre, as shudder was significant and very worrying. Pulled over on the freeway - checked tyres with pressure gauge all good. Took next exit off freeway. Car drove fine - hit a 80km/h downhill stretch 10 mins later - cruised without any power or brakes, shudder occurred again at 85-90. No warning messages, no beeps, no warning lights.

Called Lexus the very next day to alert them. Dropped the car in the following day. Gave an inspection and drive test. Said it was some unbalanced tyres. They rebalanced all 4 tyres and re-checked the recent alignment. Embarrassed because I said it was more than unbalanced tyres, because that doesn't happen randomly or all of a sudden. Have driven at >85km/h a few times since even on same stretch of freeway - all good......

But today on the freeway, same thing happened again. Called Lexus who asked me to drop the car in. Went with a long test drive with Chief Technician - and typically it didn't occur for us!! Afterwards, they ran a diagnostic on the engine, no codes or messages came up. Also checked transmission fluid colour and viscosity - all good. Driveshaft also inspected at my request. All fine.

Due to its complete randomness I have ruled out brakes, suspension, steering and wheels (all freshly balanced and aligned). Lexus said if it was a lead or plug it would be happening frequently and come up with a warning message on the dash, as well as come out in the diagnostic report.

Three things perhaps - 1. bad fuel (but I have filled up a few times over this period at different outlets);2. it's transmission related (torque converter maybe??). But to have bad fuel (water?) impacting performance on just three occasions over 4 weeks and at high speed seems unlikely. So do I have an issue with the transmission? - despite Lexus giving it the all clear. 3. The other thing I thought (and thought initially after Lexus replaced a weeping seal on the driveshaft at the 75k service) was a misaligned driveshaft. Perhaps it is random slipping out of alignment occasionally and when I hit 90km/h it causes the effect of wobbling the wheels. Then perhaps the driveshaft slips back into alignment and therefore no problem. They did allegedly look at the driveshaft and said it was fine.

Any ideas - would love your thoughts. Lexus are completely baffled, as am I!

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Check this out.


Chris, you said,

its electrical inductance. what happens is there is so much current running through the ballast it creates like an electrical magnetic field around it. . . in turn messes with all other electronic components near it.

So I assume that this only occurs when the lights are on. (Or can there be sufficient current running through the ballast, even when the lights are off?)

Sapphire Cam, does this only happen at night?

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Thanks for the quick responses guys - but no after-market HIDs - standard factory halogen headlight assemblies. Happened twice with headlights on initially, today without! - so no link there - nevertheless a frightening wake up for owners with certain aftermarket HID setups.

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could it be misfiring under certain engine speed?

bad batch for fuel?

happened to be twice actually on my old is250

at the lights the car will shudder and then rpm will drop

it happend with bad fuel

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I'm running 98RON - currently Shell V-power.

It happened again tonight on the freeway, but given I was less panicky this time I drove for a fair bit longer through the shudder. I put it in neutral and it still did the shudder, also went into sports mode and changed up and down a gear - still did it. That little experiment probably rules out the transmission then. Opened window to try and listen to engine - sounded normal. Still no warning lights/beeps/messages. Didn't notice any loss in power, just a little bit of lag associated with the shudder (as the car is having to work harder as its running rough). Noticed as if the sound was coming more from the rear this time. After about 20-30 secs at 95-100kmh the shudder gradually subsided - it didn't instantly subside, it did over time and at a constant speed. So the mystery deepens.

Spoke with my mechanic today who looks after my wife's Subaru and he said if I could rule out the transmission (which I reckon I have done), then it could be possibly a hairline fracture in a plug lead and at speed and vibration there might be a slight loss in current to the plug, leading to some mistiming, as the graphite material in the lead moves apart and then perhaps compacts back over time. But I revved it to 4,000 during the shudder and it felt and responded normally. As baffled as ever....

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Emailed Lexus dealer to let them know this morning. They told me half as much too (no leads but coils - you learn something every day!). You're right, it might be a plug (as my old C'dore years ago after a service felt exactly the same way - shuddering, and it was a dodgy plug in that instance), but wondering why its only happening at speed. Incidentially I believe plugs were replaced as part of my 75k service, and it was only after the service that this issue has come to light. Lexus refute this (ie. dodgy plug), as the ECU would be issuing 'code' if that was the case, and there has been no code.

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  • 3 weeks later...

My first impression of your symptoms are exactly the same, a coil but that does not seem correct to me when it only happens at speed.

I would ask you to get the vibration happening again, but this time put it in neutral and coast to a stop holding the revs at the vibration point.

The reason I ask this is because if it is speed related, it may well be something to do with your airflow metering. Do you have a high flow air filter fitted?

It shouldn't make a difference at all, but if your AFM is playing up it would definately have more difficulty understanding high flow high speed low throttle conditions.

How sure are you that it is an engine vibration versus a chassis vibration?

You say it's not wheels and that you've had them balanced. You can still balance out of round tyres. I've seen plenty of out of round tyres cause similar problems too. Need to spin them up by hand and check from the outside for any raise or fall in the tread and also from the front (looking directly at the tread). I've had vehicles that have out of round tyres Randomly vibrate, I think purely as the wheels and tyres find the perfect spot occasionally and unbalance the set up.

I would remove the airflow meter and check the resistors in the intake channel for muck, should be clean and shiny. Don't use a rag or your hands just good fuel injection cleaner safe for EFI.

Let me know how you go.


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For sure, but it depends on how you determine the difference. Many ways to diagnose depending on what you think it is. It also depends on what experience you have of similar problems.

But there is nothing worse than being told your looking for an engine vibration/loss of power when really you are looking for a chassis/wheel/tyre problem which has the same effect as an engine vibration say by creating a force for the car to overcome.

They can feel very similar, and usually you can determine what side of the problem you are looking for,and the diagnostic takes a new route, as you can focus on what can cause the fault in the right place instead of guessing what it could be in both areas.

I'm not digging at dealer mechanics here, but we used to fix a lot of problems at Lexus GB HQ that the dealers just couldn't fix. That's not to say that they counldn't, just that Toyota and Lexus products are so reliable and very rarely fail badly. This creates short commings in the diagnostic techniques needed to fix these problems.

For example I would never check an injector with an oscilliscope at the dealer, but when your tracing faults that are abnormal and hard to find, you have to up the ante and employ techniques that are mainly lost at the dealer with bonus incentives and busy schedules.

Any way, would like to hear more of the symptoms so we can try and get to the bottom of it. As it says in the post, Lexus baffled!!

It's not ideal trying to fix or diagnose something over the net and even face to face with a customer. For this reason Toyota and Lexus service manuals have a distinct section of questioning that you are supposed to ask the customer to focus your diagnostic. It's not there to make you look stupid or customer feel inadequate but to determine where, how and when your symptoms occur. It is a very important part of the diagnostic and over looked more often than I would like to admit. But with the correct questions asked and the right answers given, the diagnostic can proceed easily and efficiently.

The Japanese like to call it "Kaisen" maybe the wrong spelling though!!! LoL


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Haven't been able to replicate the issue since. The very last time it happened though, I put in into neutral, revved it, dropped back a gear and so on. This time I didnt notice too much of a power loss - eventually the shudder gradually disappeared and hasn't returned.

I have had half a dozen goes at it to try and get it happening again, and haven't come across the problem since. I have been doing a fair bit of reading around on other motoring forums and a few other makes recently (Ford, BMW, Merc, Toyota) have had a few owners mention exactly the same problem. Most of them went back to a brake issue where a sticking piston may actually not be retracting enough leading to a pad that is 'dragging' - eventually the piston retracts. The car didn't 'pull' or lurch any particular way though when it happened however.

No high flow air filter fitted (as far as I know) - no mods done of my vehicle whatsoever. As I said tyres recently balanced and aligned, but I'll find some time to check them out.

I really can't ascertain whether its chassis or engine - it was difficult to determine where the shudder was originating.

Simon, thanks so much for hypothesising on where the shudder may've come from.

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Hi mate,

Whilst i'm happy it hasn't returned yet, it's not helping us find the problem.

I hear you about your brakes. If you have a dragging piston on one of your calipers you can identify this easily. Without pulling up too quickly, pull up and walk around the car and feel the temperature of your wheels. If you have a sticking caliper the effected wheel will almost definitely be hotter than the rest. There will be a very hot smell around and possible brake smoke from the effected brake. The other way is to pull up slowly as if you are going to come to a stop, but at around 5km hr, take you foot off the brake and coast to a stop. Your car should stop slowly and without a final stoppage. If you have a faulty caliper piston and it's grabbing you will find that the car will stop almost as if some one has put a brick in front of the wheel. Hard to explain but it won't slow slowly, it will come to a stop with a bit of a braking feel. Bit like a push bike, if you have a brake dragging you can feel it. Another symptom is that your car will pull to the opposite side of the faulty caliper, as the force of the overheating brake will be less than that of the working one. Friction!!

Now, you mention that you had a brake service! Can you recall if the handbrake felt considerably better after you got it back? When I mean better, more perhaps the travel on the lever was reduced!

Lexus and Toyota hand brakes are generally housed within your rear rotor. Similar to the old style drum brakes of old. Except that's all they do, just hand brake. I have instances where I have had to apply the handbrake whilst moving to test certain things. And if held on long enough you will sometimes get a shudder through the rear of the vehicle. Any rear vibration can generally be felt through the whole car, unlike front end problems which can be felt through the steering and at the front. I'm just wondering if that, after the dealer adjusted the handbrake, they were dragging just a little too much, meaning the shoes (contained within the rotor) caused excessive heat build up. From there especialy with drums it wouldn't take long at speed to create a high spot or warp in the drum. However with a few more kms on the car it's possible the shoes would have worn enough to give sufficient clearance and stop generating the heat and the wobble.

It's certainly viable given the information you have supplied, it could just be that simple.

Let me know please......


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Starting to put 'two and two' together a little here.....

Now that you mention it, the park brake was noticeably tighter immediately after the service - since then it has slackened to how I remember it through the vehicles entire 80k life. What I have noticed the last few weeks is a very faint shudder under braking at all speeds (but most noticeably when braking at 30-70km/h) which I reckon is coming from the rear rotors (well it couldn't be from the brand spanking new front rotors - could it?!). I've just gone through my entire service history (receipts, job sheets), and rear rotors have not been machined/replaced at all on the vehicle. I don't see this as unusual but I was planning on getting them looked at when my rear pads need replacing which I've been advised should be at the next service (90k). Maybe, just maybe the scenario you describe has led to a bit of recent warping on my rear rotors?

Also the shudder felt like it was more through the seat and floor (centre armrest shook and felt it more through the seat), so again perhaps pointing towards the rear? Steering wheel did not shake too much and steering performance was not compromised.

I DID notice the car smelling a little hot during this period when I was experiencing the random shudder, but it was just after coming off a 'freeway run' and on a very cold evening, so whilst it caught my attention, to the point of once even opening up the bonnet to check coolant levels and hoses - I didn't suspect anything as insidious as a grabbing brake. Wasn't a 'brake' smell as such, just hot metal - like as if the engine was running a bit hot (but all is fine there). That smell has not returned since even in same driving and weather conditions. The location of the 'smell' was hard to pin point though - walking around the car I could not locate the smell from a particular location (bonnet, wheel etc.)

So perhaps we are closing in on a possible cause, and perhaps it has self-rectified as you suggest. I'll be heading to a very good tyre centre (I know the manager and they are a pretty serious lot!) down the road from me on the weekend to give all my tyres the "once over" to rule out any 'out-of-round' as well.

Thanks for your help again Simon. Much appreciated - you're a very handy resource! I'll try those braking road tests on the weekend (I'm off interstate for work at the moment).

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That does sound promising, but it could just be a coincidence. If you felt it through the seat more than the steering it's sounding more like rear.

It's not hard to over adjust the brake, it's just a rotary adjuster with a spring latch to stop it de-adjusting. As a general rule you wind the adjuster until the hub won't turn and then de-adjust two or three sectors back. Or until you can feel no drag on the hub. Because your car is rear wheel drive however, it is sometimes hard to guage what is brake drag and diff weight. The constant quest for the mechanic to do something you can actually feel or see to show his attention to detail and the great feeling of the hand brake may of just hindered the correct adjustment.

The brake shoes themselves aren't that large and are made out of some tough lining. So with a slight drag it wouldn't take long for them to over heat.

All is not lost though, as i mentioned they are really only used for parking or hand brake turns!!?? ha ha.

They can give them a once over when you change the rotors, the heat signature from the event should still be fairly visible.

Let me know how you go, and no worries, it's been fun trying to work through it.

Safe driving!


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Reckon we could have a 'case closed' now...

Did those two tests you mentioned - both tests 'passed'. Went on a drive with some intentional hard braking - heat levels from both sets of brakes consistent. No hot smell. Rolling to a stop - all good there. No grab, no lurch, no veer. More freeway drives - all good there. Tyre check - all good there as well - tyre specialist said existing tyres were 'all round' and still in balance. Nevertheless the rear tyres were down a fair bit, and they said were getting quite hard on the sidewalls - got two new tyres (which I was going to do anyhow).

Rang Lexus dealer on Friday evening to get their tyre recommendation and spoke to them about the 'overtightened park brake hypothesis' you provided, and they said yes that have seen that happen on a few previous vehicles, and suspected that when they did the impromptu inspection for me a fortnight ago. They didn't notice it at the time - since that inspection there has been no shudder whatsoeever, so perhaps it was a case of the brake loosening back after the first few weeks after the brake service.

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