Mysterious Engine Vibration

[LS 0181158]

Since last Thursday, my 1993 LS 400 with 206K has begun to shudder when the idle is raised to 1,000 rpm. This "shuddering" is not really violent, but it IS distinctly noticeable and bad enough to make some interior trim pieces buzz or rattle. This only occurs at exactly 1,000 rpm, give or take 100 rpm north or south of that mark. At normal (warm) idle, the revs are down around 600-800 rpm and the engine is perfectly smooth. Start away from a traffic light, and you'll notice the vibration as the tach passes through 1,000 rpm. Above that point, the engine is glassy smooth, like it normally should be. The shudder returns at 1,000 rpm as the car coasts to a stop, or any time it's coasting with the revs around 1,000 rpm. Step on the gas, and it goes away. This is definitely related to the engine, not the driveline, as the issue manifests itself with the car in park or neutral as well as while driving, regardless of gear.

Additionally, at about 2,000 rpm, there is a far less noticeable "recurring" vibration, which sort of pulsates once a second. I'm assuming this is related.

A friend told me that this whole issue is due to a clogged catalytic converter or exhaust buildup, and that the car has always done this and I just haven't noticed. However, this issue is definitely new, and it started from one day to the next.

I've read about bad motor mounts, belts too tight, worn pulleys, or timing belt needing replacement. Could it be any of these things?

[mehullica]

I'd replace the 2 engine mounts and the 1 trans mount. With as many miles as you have, you feel an improvement in how smooth the car will feel.

[alsalih]

I agree with mehullica, my vibration went away with the replacement of the transmission and engine mounts (or at least it was isolated enough to where I couldn't notice it anymore).

[LS 0181158]

That sounds logical, but a bit expensive. Do you all know off hand how much $$$ I am looking at spending for this?

[nc211]

2 front mounts "engine mount" are $88 each. The rear "tranny mount" is $54, you only need one of these. Probably $150 for an indi shop to install them all for you. The tranny mount is easy as pie. The driver's side of the engine motor mount is tough to get to. I'd do the tranny yourself and pay someone to handle the engine mounts. These cars can be expensive to maintain...especially if you go to the dealership for repairs. But remember, it is 13 years old. You have to expect a few hundred here, a few hundred there over the next couple of years. If you haven't budgetted for that...then I'm not so sure this is the right car for you. They're awsome when they're right...they're great when they're almost right...they're OK when they're running...and they're broke when they're broke...

www.lexuspartsonline.com check it out for parts...or www.parts.com and drill down to lexus for a list of the other places. Don't buy parts from your dealer....too much retail markup.

That sounds logical, but a bit expensive. Do you all know off hand how much $$$ I am looking at spending for this?

[LS 0181158]

Okay, I have some further developments.

The car is continuing to do this vibration thing, but now it does it a bit more across the rpm range, and the primary vibration has moved up from 1000 rpm to about 1200-1300. It is now making a pretty disturbing racket, primarily at idle or low engine speeds. At idle, I hear a very rythmic, high-pitched and somewhat metallic "squeak-squeak-squeak" sound, which goes away as soon as rpms are raised. There are also occasional and COMPLETELY RANDOM "click-clack-clunk" sounds, and frequent, lower pitched and very bad-sounding metal-on-metal grinding, which is rythmic in nature but seems to come and go at will, regardless of exact rpm...i.e. the car can be idling, the grinding will continue for 10 seconds, then there will be a "scritch-scritch-scratch" sound and the grinding will disappear, only to return 25 sec. later. Sometimes, sitting in the car at a light, I can even FEEL knocking through the chassis as these "clunks" come and go. All this noise seems to be coming from the very front of the engine. Tonight I opened the hood with the engine running and discovered that the serpentine (drive) belt appears frayed in several places on the edges, and is riding up on the edges of at least the top two pulleys.

There are NO WARNING LIGHTS on, the power steering has always worked perfectly, there are no apparent alternator-related problems (lights dimming, accessories running more slowly, etc.), the car has never stalled or lost power under these conditions, transmission shifts fine, and coolant temp remains at its a-bit-less-than-halfway mark. Climate control on or off makes no difference, except to kick the revs a bit up or down like normal. No leaks, either from power steering pump or water pump. The car seems to have normal power and is eminently driveable at freeway speeds, although the racket can still be heard at a very muted level. The engine itself still purrs and revs very smoothly.

I just changed the oil yesterday, but have no records as to when the timing belt or water pump were last changed. Regular service procedure would have mandated this being done 26K miles ago, at 180K. I'm hoping this service was not deferred.

I must admit that this stuff happened for two days about 1,500 miles/3 weeks ago--but it disappeared over the course of normal highway driving and did not reoccur until yesterday--although the vibration I mentioned in earlier posts has been going on for almost a week now.

Given that this noise and vibration seeming to be related, I'm having my doubts about the motor mount theory, although that could be PART of the problem; it certainly would not account for this grinding and squeaking racket.

I found this Nov. 2004 thread entitled "Lots Of Bad Sounds, What Do You Think?" describing a 1990 LS with remarkably similar symptoms. Miles are similar too, at 200K.

Based on that thread, I'm thinking serpentine belt, although it would have to be coupled with a bad idler pulley or tensioner pulley. Some people on that thread mentioned a "fan bracket". These grinding noises really sound like a bad bearing(s) somewhere. One person with a great deal of mechanical experience who casually listened to the sound 3 weeks ago concluded the water pump (bearings) were probably bad. I would not be surprised if it's original from 90K, but I'm wishfully thinking it's something else.

[LS 0181158]

By the way, nc211,

thanks for that tip about www.lexuspartsonline.com. It is a great site. I've already checked--serpentine belt, $36, idler pulley, $50, tensioner, $144.

I'm 22 and since 17 I've owned an '86 BMW 528e w/250K and rebuilt engine just before I got it (drove it 40K), '90 Acura Legend LS from 150K to 201K, and '90 BMW 535i 128K to 175K. I do understand what you are saying about a few hundred $ here, few hundred there, etc. I've had to do $500-700 services on all those cars at one point or another, plus those many smaller services and realize this is normal and expected. I'm a little disappointed to be having all these problems with my LS so soon, but I know the car is not really to blame and your point is well taken. I'm more frustrated that I'm right now in a bad way financially and can't take care of these problems as immediately and properly as I'd like.

Still, I must disagree with your one comment--I've finally driven my long-coveted Lexus LS 400 and know this is definitely the right car for me! :-) I just might have picked the wrong time to get it.

Any ideas about my above post are so appreciated--sorry for the length.

[LS 0181158]

Well, the problem is fixed.

Not water pump, but FAN BRACKET.

Check engine light problem is back, though--please see my new thread ("How to remove ECU") here if you have ideas.