Engine noise when accelerate

[vissine]

Hello everyone, my car makes noise again. When it is cold in the morning, the car is idle with around 1400 rpm at first and the noise sounds like coming out from the back of the engine. When I drive it, the sound is noticeable at 1400 - 2200 rpm when I accelerate from stop or from low speed. It goes with engine rpm, not the car speed. What is the possible cause? Actually, the noise is also noticeable during the day but definitely much better than in the morning when it is cold. I am thinking about EGR pipe, MAF, or EGR temperature sensor but want to check if it makes sense. 

[Lexus Owners Club]

what sort of noise is it generating and is it engine speed related?

[vissine]

The sound is like rattle noise. Yes, it is engine speed related as mentioned above.

[Lexus Owners Club]

try disconnecting the auxiliary drivebelts and running the engine for a very short time as this can be a common problem with cranshaft pulley breaking up....if the noise disappears then this could be it

[vissine]

Thanks for getting back to me. I removed the drivebelt on Sunday hoping the sound came out from powersteering or alternator but the noise was unchanged. Does the MAF have anything to do with sound? The sound is generally at the end of the engine and near the firewall makes me think about the infamous broken EGR exhaust pipe but the sound is not like hissing air leak. I don't know what to do now so I leave the Lexus alone and drive my back up car.

[Lexus Owners Club]

I don't believe the MAF would have a knocking sound to it although if the trunking is split then it would be a blowing / thudding noise.

The EGR would be a totally different sound so not sure that would be the cause.

I think it may be worth trying to use a smoke tester to see if there are any cracks in exhaust, inlet manifolds or EGR to eliminate those components

[vissine]

I think the noise comes from transmission area. In the past, when it happened, the noise went away after I changed transmission fluid. I think this happens again. It just doesn't make sense that It happens again after only several thousand miles. I will wait until after the holiday to change the fluid and see how it goes.

Thanks Trevor, I have not touched the EGR and MAF yet. 

[vissine]

So, I change the fluid (drain and fill 2 qts) and it seems to help a bit. The noise occurs in the morning when I start up the engine and gone in maybe 5-10 minutes. There is nothing wrong with shifting or accelerating. Is the transmission pump failing and is there an instruction to replace one?

[Micah.Berry]

I wish I could help more here, but from what I read - you sound like you're on the right track.  Consider the transmission holds considerably more than 2 quarts, and with a drain/fill, you're only changing the portion that is in the drain pan, not the amount still in the transmission gears, tubes, torque converter, etc.  You might think about changing again to get additional new fluid in.  Also - are you using the correctly specified fluid?

[vissine]

Thanks for making sure that I am not getting off the rail.

Yes, after the second change, this time I replace the transmission filter. the car is quiet now. From looking at the filter, there are debris that were clogging it up. I think the transmission is reaching near to the end of its life. I don't remember reading anyone's post about transmission filter clogged with debris on this site but that's what happening to my car right now. After the filter has been changed, it runs smooth and quiet like there is nothing wrong with the transmission. Up to the point it started to clog up the filter, I was only using Toyota T-IV bought from local Toyota dealer. But now, I am switching to synthetic since type T-IV is not anything special anyway. 

Part 1 is done, Part 2:  I will change the transmission filter again after 1000 miles and hope that the debris is no longer an issue. After that, I should be a happy driver until it happens again.