Light Knocking At Idle - Doesn't Happen When In Gear

[prix]

94 LS400, about 96K miles now...

I thought an oil change would fix the light knocking sound that I've been hearing for several months now, along with a noticeable 'chatter' when I press on the gas pedal or take my foot off of it (throttle opening up, I guess). That was done in December but I am still hearing the light knocking or 'chatter'.

Yesterday, on a drive back from an outing, after I pulled over and parked, here's what I noticed:

Car in gear at low idle, no knocking. Very quiet, in fact.

Car in park or neutral at low idle, I hear light knocking.

I sat there, letting it idle and shifting through and listening. It was consistent. Neutral or Park it makes light knocking noise. In gear, it doesn't.

Which does this point to...a throttle body cleaning OR transmission fluid change?

I know throttle body is overdue for a cleaning.

The trans fluids are due (but probably could be let go awhile longer).

[steve2006]

Difficult to say without hearing the noise but could be a loose exhaust heat shield rattling any where on the system.

Have you lifted the hood to see if you can locate the noise more accurately or been under the car?

[prix]

Thanks, no even though I read these forums, I am not set up to DIY. I am lining up a bunch of work in prep for passing a smog test, so maybe I'll add this to the list. In some of my reading, it says 'light knock' can be normal, but since it wasn't there before, I would like to get rid of it if possible. Let's see what happens when I change a bunch more fluids out and clean the throttle body. I will post back if I think of it.

Difficult to say without hearing the noise but could be a loose exhaust heat shield rattling any where on the system.

Have you lifted the hood to see if you can locate the noise more accurately or been under the car?

[landar]

I am leaning towards engine mounts which might let the engine bang or clank against worn mounts when unloaded in park or neutral but held more in place when torqued slightly being in drive. Maybe even worn transmission mounts.

[prix]

Just from the sound of the noise, I thought it was an internal issue, but you may be on to something, and here's why.

I was looking under the hood the other day because I was having that battery tested again (go figure, they are saying it's fine). And while there, besides noticing that line of oil along the valve cover, I also noticed that where the valve cover is closest to the firewall/near the front windshield, it seemed to be sloping down or sagging. In other words, it didn't seem to be sitting level. I walked around to the right front fender, standing crosswise, and eyeballed it again, just to be sure. It looks to me like there's some sag in the back. Is that typical of bad mounts?

I know I need front lateral arm bushings (those are sagging), but it was an expensive repair, and I was told at the time that if I didn't replace them the only thing I would notice is that I'd feel the road and bumps, etc. Would that needed repair cause this sagging? Or is what I am describing caused by bad mounts?

My repair list is growing by the day! Thanks for any input.

I am leaning towards engine mounts which might let the engine bang or clank against worn mounts when unloaded in park or neutral but held more in place when torqued slightly being in drive. Maybe even worn transmission mounts.

[billydpowell]

if it were mine, first thing I would check is the torque convertor to flywheel bolts. that is how they would act.

[prix]

Ok, will do. Take a look at the top photo here (the ignition).

http://www.lexls.com/tutorials/electrical/instrumentcluster.html

See how keyhole and thick rubber surround is perfectly flush with and exactly centered in the housing? Well, my car's ignition doesn't look like that. If you look at it head on, it looks like someone pushed it in on the lower right. It looks a little canted (turned in toward the engine) and a little off center (in its housing). I emphasize 'a little' off because it doesnt look like it's getting ready to collapse inward or anything...it's not tha bad, but it's definitely noticeable. As if some weight has caused it to twist a little.

IF I am right and that is sagging that I see in the back of the valve cover (and it's not my imagination), then maybe it's related to an ignition that is slightly 'twisted' in its housing? Going to look up torque converter now.

if it were mine, first thing I would check is the torque convertor to flywheel bolts. that is how they would act.

[prix]

After looking up torque converter, I take it that you were addressing the knocking/chatter sound, not the sagging issue? Can you please elaborate on why you think a torque converter could be involved. Even at salvage yard prices, it's not cheap. Tx.

if it were mine, first thing I would check is the torque convertor to flywheel bolts. that is how they would act.

[billydpowell]

After looking up torque converter, I take it that you were addressing the knocking/chatter sound, not the sagging issue? Can you please elaborate on why you think a torque converter could be involved. Even at salvage yard prices, it's not cheap. Tx.

if it were mine, first thing I would check is the torque convertor to flywheel bolts. that is how they would act.

Yes, I was referring to the knock, and was only remembering how loosened bolts would make a knocking sound like that. no sound under pressure (in gear) but knocking at idle, and along with a noticeable 'chatter' when you press on the gas taking off. all you would need to do was to tighten the bolts, not replace anything. That has happened 4 or 5 times over the last 30 years that I owned my shop, so I just mentioned it, as something to check..

[landar]

It could be as Billy suggests but checking and tightening the flywheel(flexplate) to TC bolts would require pulling the tranny or engine, would it not? If so, that would be a lot of work.

To check if the clanking might be the motor mounts, try to isolate the noise while it is idling. I would even pry a large crowbar against the engine block to see if that diminished the noise as that would help to keep the engine from jumping around(if it is mounts) and might give an additional clue.

[billydpowell]

It could be as Billy suggests but checking and tightening the flywheel(flexplate) to TC bolts would require pulling the tranny or engine, would it not? If so, that would be a lot of work.

To check if the clanking might be the motor mounts, try to isolate the noise while it is idling. I would even pry a large crowbar against the engine block to see if that diminished the noise as that would help to keep the engine from jumping around(if it is mounts) and might give an additional clue.

Landar you are probably right, I didnt think of that, I thought there was access to the FW/TC area from below.... never looked at that.. sorry.

I noticed this photo, would that not let you have access to the bolts??

for some reason I cant put a photo in here, will do so below..

[prix]

I'll want to try the smaller 'fixes' first, so this goes on the list (crowbar test).

Also, a day after I topped off the oil with about a third quart of 10w30 (remember I said it was a tad low)...and I put in 10w30 by accident...it takes 5w30...when I drove the car a day later, the knocking and growly noise on acceleration and deceleration seemed less loud. It's still there, but muted. The weather was also a little cooler (we've been having some 75 degree days here in Southern California), maybe by 5 degrees or so. I did not put in a lot of 10w30, so I don't know if that would have had any impact.

If I were to take it in to the dealer, what kind of tests would they use to check motor mounts (engine, transmisson)? I'm not taking it in, but was curious whatis their method of diagnosis.

It could be as Billy suggests but checking and tightening the flywheel(flexplate) to TC bolts would require pulling the tranny or engine, would it not? If so, that would be a lot of work.

To check if the clanking might be the motor mounts, try to isolate the noise while it is idling. I would even pry a large crowbar against the engine block to see if that diminished the noise as that would help to keep the engine from jumping around(if it is mounts) and might give an additional clue.

It could be as Billy suggests but checking and tightening the flywheel(flexplate) to TC bolts would require pulling the tranny or engine, would it not? If so, that would be a lot of work.

To check if the clanking might be the motor mounts, try to isolate the noise while it is idling. I would even pry a large crowbar against the engine block to see if that diminished the noise as that would help to keep the engine from jumping around(if it is mounts) and might give an additional clue.

[prix]

All good. I want all options on the table. For all I know, this is 'normal' as the car is getting older. What about valves knocking? I was looking that up (valve adjustment) and I'm at 95K approx and I don't think that has ever been done. I will have to comb through the records. Read it's kind of a big job...I would have to plan out for that, but could get that done if/when they fix the valve cover gaskets (I wiped off that line of oil and am watching for any reappearance...might be a very slow leak). In the meantime, having bolts snugged down as you suggest. Tx.

It could be as Billy suggests but checking and tightening the flywheel(flexplate) to TC bolts would require pulling the tranny or engine, would it not? If so, that would be a lot of work.

To check if the clanking might be the motor mounts, try to isolate the noise while it is idling. I would even pry a large crowbar against the engine block to see if that diminished the noise as that would help to keep the engine from jumping around(if it is mounts) and might give an additional clue.

Landar you are probably right, I didnt think of that, I thought there was access to the FW/TC area from below.... never looked at that.. sorry.

[1990LS400]

For all I know, this is 'normal' as the car is getting older. What about valves knocking?

A bit of valve chatter is quite common on the gen 1 LS400 as they age. My 90 LS did the same thing for many miles before I sold it but I only noticed it at idle. My mechanic didn't think it was worth trying to fix so we never tried and I didn't find it bothersome. I sold the car to a coworker in 2003 after driving it from new to 183,500 miles. The guy I sold it to recently advertised the car at 295,000 miles on Portland OR Craigslist using the phrase "Drives amazing!" so it apparently continued to run.

[billydpowell]

I tried to post this above, no luck, so here it is. Landar this is your photo..

cant you turn the flywheel and tighten the bolts from here?

[prix]

Can someone give me an estimate of how much time it should take for an indie mechanic to do all of these things? .

Clean Throttle Body (completely remove and clean)

Replace Air Filter

Clean EGR (just the 'core', which I assume means you don't have to remove?)

Clean MAF sensor

Clean IACV

[Note: I meant to post this in the 'smog test thread', but accidentally posted it here...oh well...anyone?!]

[landar]

I tried to post this above, no luck, so here it is. Landar this is your photo..

cant you turn the flywheel and tighten the bolts from here?

Yes, I do believe you are correct, Billy. For some reason, I was thinking of the flexplate to crankshaft bolts. My mistake.

[billydpowell]

Can someone give me an estimate of how much time it should take for an indie mechanic to do all of these things? .

Clean Throttle Body (completely remove and clean)

Replace Air Filter

Clean EGR (just the 'core', which I assume means you don't have to remove?)

Clean MAF sensor

Clean IACV

[Note: I meant to post this in the 'smog test thread', but accidentally posted it here...oh well...anyone?!]

look over here and you can tell" http://www.lexls.com/tutorials/EFI/throttlebody.html

[prix]

Got it. Btw, I've decided I am not touching that MAF sensor...since it's a Karmen Vortex and the CRC Mass Air Flow Sensor Cleaner has a warning not to use it on certain Lexi :-). But looks like just to clean the throttle body could easily be an hour.

Can someone give me an estimate of how much time it should take for an indie mechanic to do all of these things? .

Clean Throttle Body (completely remove and clean)

Replace Air Filter

Clean EGR (just the 'core', which I assume means you don't have to remove?)

Clean MAF sensor

Clean IACV

[Note: I meant to post this in the 'smog test thread', but accidentally posted it here...oh well...anyone?!]

look over here and you can tell" http://www.lexls.com...rottlebody.html