BridgePrt

2008 LS 460 I recently replaced the left side air fuel sensor due to an engine code. But then a week later started getting P0420 cat efficiency below threshold error. I guess in the few weeks it took to fix the AF sensor my cat converter got clogged. I tried the quick fix fuel additives but it did not help. And then slowly a rumble started to appear, and now the rumble has gotten crazy loud. It happens when transmission is in a high gear and RPM is around 1300 with very slight pressure on gas pedal (flat road, usually going 40 mph in a high gear.) If you give it more gas the rumble goes away. Its only during slight load and 1300 rpm. I lifted the car and made sure all the bolts for the under engine protectors were in place and tight. I did notice the aluminum rear cover near the transmission does seem to vibrate when I hit it with my hand but all the bolts are secure. I'm wondering if a slightly clogged catalytic converter could cause this rumble. It seems somehow related to engine rpm or transmission load. As a work around I've been manually shifting and driving in traffic in 3rd or 4th gear to keep the rpm higher. Hopefully someone reading has an idea or best guess about this issue. I'm really going to hate replacing the cat converters and was hoping to drive the car a year more and just trade it in.

Nospinzone

I have a 2007 and never experienced anything like that. I can't imagine what is causing it, but I really doubt it has anything to do with the catalytic converters.

Cape600L

is it AWD? Either way, check all of your axles and look for torn CV boots. Also driveshaft center bearing.

swfla

iTrader: (1)

It's possible that the pre and post cat sensors aren't working right and the converter is OK. I imagine a replacement sensor is much cheaper. Lots of things can produce a rumble. Get another OBD2 reading, it may tell the source. Hope it's not the transmission, but it could be.

hfahmy

Do u have any other codes?

swfla

iTrader: (1)

Instead of assuming what the issue is, get your car to a mechanic who specializes in Japanese cars. A Toyota/Lexus expert would be best. Modern cars are computer controlled in a very complex balance. I'd hate to see you throw money and resources at the wrong systems. Let us know how this problem is resolved.

BlazeViper

This is unbelievably similar to what mine is doing. I have both cat codes for system below efficiency and have this awful vibration/ low frequency boom at 1400-1600 rpm under light load.

The low frequency can be heard through the entire cabin and is even worse for the rear passengers.

Vansibel

Did you buy the car out of Texas ? Check for rust hole in your mufflers https://www.clublexus.com/forums/ls-...ssage_10273321

BlazeViper

Oh lord, my car came from Manitoba, that would make a lot of sense.

BMo5

I'm having the exact same issue and I have had a lot of input on my thread. I did a lot of my own looking into it - couldn't figure it out, so I took the car into a mechanic. They were also baffled. We're thinking drivetrain related. Because it is RPM related and not speed related, I was starting to think transmission, but everyone agrees it's coming from the rear so I'm not sure.

I changed the rear diff fluid and that made no change. I needed new tires anyway, so I did that. No change. Just to rule those out. I have no codes, btw.

I'm now looking at the flex couplings on the driveshaft. Sadly, you cannot buy them without buying a new driveshaft at near $1k. I don't think it's the engine mounts - the engine isn't jumping when powerbraking. Take a look at those couplers and see what yours look like.

I'd be happy to work with you to figure this out.

John1320

My car started doing the exact same thing a week ago without any warning lights. It happens when transmission is in a high gear and RPM is around 1300 to 1500 rpm with very slight/steady state pressure on gas pedal (flat road, usually going 40-50 mph in a high gear.) If I give it even slightly more gas the rumble goes away. if I give it less gas the rumble goes away. if I keep the gas exactly the same then shift it in to manual it goes away. Was anyone able to find the cause of this issue?

I need to reiterate that this is a serious whole car heavy bass sounding rumble which can be felt throughout the car. it's not coming from any of the 4 corners. after trying to diagnose it while driving for the last week there is a very specific set of variables that needs to be met when it happens as stated above.

I'll check my engine mounts tomorrow since i'm off work. I was thinking the rotary-dirdir was to blame or maybe my headlight fluid was low again. i've already fixed/replaced so much crap on this car. when it's working it's awesome. when this type of **** happens I grow tired of lexus engineering very quickly.

Any input would be greatly appreciated!!!! A Flatout problem-solved fix would be godlike! I haven't hooked my techstream to the car in a while (4 months) because there are no lights in the dash.

swfla

iTrader: (1)

It's too bad the OP didn't post his solution. I recall photos of 460 mufflers rusted out on the top side. Can't be seen until you drop the muffler. Just another thought. Suggest you check for codes, there are many that don't trip a dash light. Also several times I've read of loose heat shields rattling at specific rpms. Engine and trans mounts do go bad on the 460.

BMo5

At shift points (around 1300rpm) the torque converter locks in or unlocks to shift gears either up or down respectively. That shudder can occur due to problems with the torque converter lock. That shudder is the lock trying to engage. I replaced my torque converter and that fixed it but that meant removing the exhaust which caused other issues with sensors and was very expensive. In short, i recommend performing the 3x fluid change first. It'll likely fix the issue without being too invasive. It'll cost a few hundred but it's far cheaper than a new torque converter @ $1000 just for the part plus the fluid. In hindsight, I wish I had just done the fluid change. But if a fluid change doesn't fix it, a new torque converter might be needed. That's a lot of work and will cost several thousand. Good luck.

Cape600L

I occasionally have a similar issue. Was told by a Toyota tech to have the memory/adaptations cleared for the transmission module. I have not taken the time to take to dealer to do that, but he seemed to know exactly what I was talking about and hence his recommendation. Just an FYI.

swfla

iTrader: (1)

Resetting module, fluid exchange are all great suggestions and low cost maintenance. Another issue that has come up is harmonic vibration in the drive shaft. Several posts about it. Sometimes it's worn U joints and/or brackets causing the vibration. The more complex a car is, the more difficult trouble shooting can be, unfortunately.