lexus94ls

Last night, my 1994 LS400 was running beautifully - then it started making a grinding noise under the hood, and 'tugging' at the engine - RPM change like a misfire. I immediately thought of all the obvious:

1.) Water Pump - engine running at normal temperature, no coolant leaks or steam.
2.) Power Steering Pump - power steering running normally with no extra noises.
3.) A/C Compressor - air conditioning is normal and runs cold.
4.) Alternator - no whining sounds from alternator and charging normally.
5.) Drive Belt - appears normal and not loose or burning.

At this point I'm thinking it's the Idler Pulley? I did notice little particles of metal that have gone onto some of the plastic surfaces under the hood. Did the Idler Pulley Bearing fail?
There is a grinding, rumbling noise and occasionally will tug on the idle. (I know that's a bad description but it seems like something binds and causes the idle to drop momentarily, almost like a misfire). Engine is running clean, no smoke. My worst fear is the Timing Belt, but the engine will start quickly and normally, and seems smooth if revved up a little. The sound doesn't seem to get louder with increase in engine speed. The only thing I had noticed earlier last night before this went crazy was a little squeaking noise like a bearing getting dry. Unfortunately I didn't pay attention to it at that time because the car was driving SO well last night!

What do you think? I'm pretty mechanically inclined, but this is my first Lexus. And now this morning it sounds so bad that I don't want to risk driving it.. To me, seems consistent with a bearing that has gone bad - but where?

lexus94ls

OK so no advice LOL. I'm thinking I'm going to first try taking off the serpentine belt and running it for a short time, see if the problem disappears, that would at least rule out engine issues...?

Lexusdk

If you have a stethoscope or a super long flat head screw driver, start probing around the engine to determine where the sound is coming from. Does the sound change with the rpm?

Lexusdk

I just re-read your original post. So the sound does not change with the rpm. But definitely try to probe and listen if you can pinpoint the sound. I've had ones with a bad idler pulley, water pump and alternator bearing.

oldskewel

iTrader: (1)

"Fan bracket" is a common failure on these cars. Search on here for that term. It's the bearing supporting the fan. Good luck.

lexus94ls

First of all, thank you to everyone that replied. I got the serpentine belt off and started the engine, no noise - so apparently not the water pump. I then set about checking all the pulleys for smoothness and end play, appears to be just the Idler Pulley thankfully! Will be replacing it tomorrow and keeping my fingers crossed...

lexus94ls

Well I was wrong. The Idler Pulley didn't look like it could have caused metal shavings, and it didn't. It's that Fan Bracket thing. Going to be a more major repair than I imagined unfortunately. I've started to remove the Fan Bracket but there's apparently more to it than just a simple unbolt. I'm going to do the search here for it.

oldskewel

iTrader: (1)

Here's a head start on the procedure:
http://www.lexls.com/tutorials/engine/timingbelt.html

The fan bracket replacement is about half way through a timing belt replacement. You'll find deeper discussion here when you search. Again, good luck.