Herm

1993 LS400 90k miles. I noticed that on startup there is sometimes what sounds like a slight rumble just when the the engine starts to run. Is this normal ? Does it mean that something is going to fail soon ? Could it be a slight backfire ? Appreciate ant thoughts - Herm

tvd51

Mine (91 LS400 with 150K) makes a clunking noise - louder when it's cold - at startup (the moment the engine engages) and the Lexus mechanics suggested that the drive belt (aftermarket) and the idler need to be replaced. Another possible cause is the engine mount. I'll replace the belt & idler soon (USD 300 for parts).
tvd51

Herm

Interesting, Thanks for the info - I'll watch the engine on startup and see if it "jumps" when the sound happens, which could indicate an engine mount problem. If it was a bad mount I think there would be other noises while driving ?

Concerning the drive belt / tensioner you mentioned: I would think that you could tell if the tensioner is bad by checking a mark that indicates proper tension (I'll look in my service manual tonight and let you know). --- Herm

tvd51

The tensioner and the belt tension are OK, but the idler (a different piece) is seized sometimes. If the engine mount is worn out, you'll notice more at startup and hard braking/acceleration than when the car is steadily moving.
tvd51

GA400

mine was making an odd noise at startup intermittently just before the water pump went out last year. a bearing seized in the pump a couple of weeks after the sound started.

Herm

Thanks - Water pump and Timing belt were replaced on this car about 40k miles ago so I hope that is not the problem. Are water pumps known to fail often (40k) ? --- Herm

5ofakind

not likely unless your serpentine belt is too tight which then may cause excessive wear & tear on bearing inside water pump.....

Look to your engine mounts as the culprits here...........

Jeff

tvd51

I just replaced the drive belt and the idler yesterday and the car still makes the same clunking noise at startup. I guess the next thing I should look at is the engine mount. Anything else ?
tvd51

VVT-i

Herm, my best guess is your starter goes bad. After the engine started to run and you let go of the ignition you disengage the start solenoid/gear, so the noise stopped. But this's just my guess without hearing the noise in person.
If the water pump or idle pulley goes bad, it will make noise all the times not just when you start the car. Good luck.

tvd51

In fact, the noise happens right after the starter stops, exactly at the moment the engine engages. All I can think is the engine mount or flywheel.
tvd51

tvd51

VVT-i: After replacing drive belt & tensioner, and checking engine mounts, my Lexus dealer thinks that the clunking noise at startup could be at the starter, but I don't understand why it makes the noise when the solenoid/gear disengages.

Does it mean that I have to replace the starter soon ? It would be a labor intensive job.

tvd51