Hi everyone would love some thoughts and input on this issue. We have a 2002 LS 430 with about 233K. When accelerating, it’s been making a knocking or diesel like noise. When you take your foot off the gas, the noise goes away. I’ve recently replaced both knock sensors with factory Toyota sensors, I always run 93 octane, and I currently have no CELs showing. What could it be? Your thoughts are appreciated! I’ve attached a video here so you can hear what it sounds like.

 

I couldn't hear anything on your video. Certainly not a knocking sound.
I could hear a kind of rumble that sounded like either an exhaust leak or tyre noise, but difficult to be sure.

 

We are currently on a trip in the mountains and the noise seems to be getting worse. It’s a loud knocking type of noise and seems to happen mostly going up hills and between 20 to 40 miles an hour or so. Here’s a video I took today, if anybody has any thoughts or advice that would be great!

Edit: the video does not seem to be uploading so I will try it again tomorrow so

 

Are you running premium fuel? The sound you are describing and the conditions sounds like pre-detonation or knocking. Really not good for the engine. Get yourself a bottle of Marvel Mystery Oil and put about 1/2 in when tank is empty to help clean the tank and injectors and run premium. Then the next half on the next tank.

 

A very common cause of metallic rattling, upon rough idle or acceleration: metal clamps holding the heat shields to the exhaust pipes. I had this exact problem years ago.

Crawl underneath the car and wiggle the clamps and heat shields. If any are loose, just rip them off and remove the heat shields. Bonus side effect: you will prevent premature Y-pipe failure codes P0420 and/or P0430 by removing the heat shields, preventing salt accumulation between the shield and the pipe, and preventing galvanic corrosion (dissimilar metals contacting each other). Unfortunately, I didn't know about this until it was too late, so I needed a new Y-pipe. Obviously I opted not to reinstall the heat shields onto the new pipe.

 

your description sounds like mild detonation or possibly the variable valve mechanism rattling

do you have a elm327 code reader/ datalogger?

If would help if you could record a trip when this is occuring with engine temp, maf, tps, rpm both ltft's, and both o2 sensor 1.

 

Wild guessing here but perhaps carbon build up is causing pre-detonation. The ECM should be adjusting for fuel type to minimize or eliminate pre-detonation. I have only heard my car knock once for about 30 seconds and that was lugging the engine up a long steep hill in very hot weather when I happened to be running a tank of 87 octane. Since that point I have only run 91 octane or higher during summer months and have never heard the engine knock again in any situation.

I'd do the simple stuff first like running an fuel system cleaner for a couple of tankfuls. Also maybe try an octane booster in the current tank - maybe you got some bad or mislabeled gas.

 

Thank you everyone, for the input and suggestions. I keep trying to upload this video and it just won’t work :-( To answer a few questions posed above: I always run 93 octane and currently have no CELs showing. It sounds like it could be valves rattling? I have just filled up with some ethanol free 93 octane to see if that makes any difference. I recently had the MAF cleaned. To Aus430 - I don’t own a code scanner myself.

I also plan to take it to the mechanic next week, hopefully I can get it to make the noise with the mechanic so they can diagnose it. Thanks again!

 

if you want us to watch the video, put it on youtube

 

Don't neglect the engine temp sensor in high mileage and older cars. They don't fail like other sensors and give a code. They just start sending incorrect temp readings and these are factored in for the air to fuel calculations. They are pretty easy swap. This sensor is not what you see at the cluster. That is a separate sensor.

 

If I had recently got the MAF cleaned and then this issue just started, I'd be very tempted to buy a new MAF and see if that fixes the issue. I know folks don't like to throw money and parts at an unknown problem. Installing a new MAF takes literally 5 minutes. Just buy one from a source that has a decent return policy so you can easily return it if the problem persists with the new MAF installed.

 

Only way to clean the MAF is to spray with MAF or electronic cleaner. Don't want to touch it. And that is if you have the wire sensor. If it's the light sensor don't touch it at all. They also go bad. If the MAF is going bad it would run bad. Normally you would have a code and you would experience it consistently, IMO.

 

That is interesting.

Do you knot where is the cluster sensor located?

 

did you figure out what it was ?

 

Did anyone DIY the replacement of the rear manifold/cat? Doesn't look like an easy job at all.