Vibrations when sitting in drive

Aukland

Original poster
Member
Jan 12, 2012
50
Hey everyone. I have an 02' Envoy 4.2 4x4 125k.

When I am stopped at a light the voy vibrates. Not just the normal barely noticeable vibrations you get from the vehicle running, it is a moderate vibration that goes away when u put the vehicle in park or neutral. This is causing me to think it is something within the trans :sadcry:. Any idea's or other people experienced this problem?? I will try to get more deet's/better description tonight when I have access to it (she drives it :duh:)

If you need more info as I know this is very broad let me know and I will check it out tonight. Thanks!
 

HARDTRAILZ

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Nov 18, 2011
49,665
More than likely you should give it to me

But have you cleaned the throttle body since you got it?
 

Aukland

Original poster
Member
Jan 12, 2012
50
Have not cleaned the throttle body yet. I can give that a go this weekend.

How could i confirm it possibly being the motor mounts?
 

The_Roadie

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Nov 19, 2011
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Portland, OR
If the RPMs stay constant, and the vibration is exactly 10 Hz, it's motor mounts. If it reduces with higher temperature, it's confirmed. I recommend looking at the plastic intake manifold housing on the driver's side and see if you see the rotational vibrations worse there, about 1/4" or more, that's another clue. Some folks have tried to pry up on the passenger side motor mount (usually the one in worse shape because of the nearby exhaust manifold) with a pry bar and if the vibration changes its nature, that's positive confirmation.

Always have somebody you trust on the brakes while you do an underhood experiments in DRIVE with the brakes on.
 

Pittdawg

Member
Dec 5, 2011
538
the roadie said:
If the RPMs stay constant, and the vibration is exactly 10 Hz, it's motor mounts. If it reduces with higher temperature, it's confirmed. I recommend looking at the plastic intake manifold housing on the driver's side and see if you see the rotational vibrations worse there, about 1/4" or more, that's another clue. Some folks have tried to pry up on the passenger side motor mount (usually the one in worse shape because of the nearby exhaust manifold) with a pry bar and if the vibration changes its nature, that's positive confirmation.

Always have somebody you trust on the brakes while you do an underhood experiments in DRIVE with the brakes on.

How do you know if the vibration is 10hz? When you feel the vibration, is it in general or more specifically in the go pedal?
 

Aukland

Original poster
Member
Jan 12, 2012
50
the roadie said:
If the RPMs stay constant, and the vibration is exactly 10 Hz, it's motor mounts. If it reduces with higher temperature, it's confirmed. I recommend looking at the plastic intake manifold housing on the driver's side and see if you see the rotational vibrations worse there, about 1/4" or more, that's another clue. Some folks have tried to pry up on the passenger side motor mount (usually the one in worse shape because of the nearby exhaust manifold) with a pry bar and if the vibration changes its nature, that's positive confirmation.

Always have somebody you trust on the brakes while you do an underhood experiments in DRIVE with the brakes on.


Very much appreciated. That one will wait till the weekend where i can pull it into a decent area and work from there. RPM's on start up are a bit above 1k then lower as it run's. Didn't know if that also had any relevancy to this matter (could be something entirely different, Maybe a vacuum leak?)
 

Sparky

Member
Dec 4, 2011
12,927
I'd do a visual inspection of the mounts first. In my case it was pretty apparent my mounts were shot. The driver side didn't look all that bad, but the passenger side one had a split in it.
 

Pittdawg

Member
Dec 5, 2011
538
Sparky said:
I'd do a visual inspection of the mounts first. In my case it was pretty apparent my mounts were shot. The driver side didn't look all that bad, but the passenger side one had a split in it.

You don't have pics do you?
 

The_Roadie

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Nov 19, 2011
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Pittdawg said:
How do you know if the vibration is 10hz?
Get out your electronic stoboscope? :wink: Borrow a high speed camera from Mythbusters? :cool:

Aukland said:
RPM's on start up are a bit above 1k then lower as it run's. Didn't know if that also had any relevancy to this matter (could be something entirely different, Maybe a vacuum leak?)
Normal start-up idle RPM does indeed go down as coolant temperature comes up. This is the table built into the PCM:

idle.jpg
 

STLtrailbSS

Member
Dec 4, 2011
1,617
"His name is Roadie hes the local genius around here dont question his answers" lol just had to add that in because he knows what hz a motor mount failure vibrates at.
 

floridafitz

Member
Jan 2, 2012
151
Winter Springs FL
The 2003 4.2 I6 models (or at least mine) had gel filled mounts...maybe 02 as well. Two of my mounts failed at about 100k and the gell began to ooze out. Dealer changed out all three counting the tranny mount. No vibration since.
 

Aukland

Original poster
Member
Jan 12, 2012
50
Thanks everyone for the help. It's getting rly cold and high winds didn't allow me to do much. But there are no noises in park reverse and neutral. 1, 2, 3, and drive it makes the noise. I will see about visually checking them this weekend as well as clean the fb see if that helps anything. And thanks Bill for the rpm chart.
 

Aukland

Original poster
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Jan 12, 2012
50
Tb. Sorry it won't let me edit on mobile lol
 

The_Roadie

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STLtrailbSS said:
...he knows what hz a motor mount failure vibrates at.
Thanks for the kind words. But just so nobody thinks I'm a magician (just an engineer), the vibration in DRIVE comes from a simple harmonic (rotational) system made up of the mass of the engine, transmission, and drivetrain, and rear differential. When you go into park or neutral, that removes the mass of the rear driveshaft, differential, and axle shafts from the system. The natural vibration frequency of a system depends partially on its mass and the mounts. If the natural frequency is the same as the frequency that it's being "excited" (pulsed) at, the vibrations don't damp out and average to zero. They grow and grow until they annoy you.

10 Hz just happens to be the same as 600 RPM, the usual warmed-up idle speed. :wink: You can also reduce the vibration by changing your idle RPM to 750 temporarily, which I did as an experiment with EFILive while I was troubleshooting my own motor mount problem.

Aftermarket motor mounts are not duplicating exactly the OEM units in terms of viscosity and stiffness, which is why they often fail to solve the problem. That's why we always recommend OEM mounts, no matter what the price.
 

Pittdawg

Member
Dec 5, 2011
538
the roadie said:
Thanks for the kind words. But just so nobody thinks I'm a magician (just an engineer), the vibration in DRIVE comes from a simple harmonic (rotational) system made up of the mass of the engine, transmission, and drivetrain, and rear differential. When you go into park or neutral, that removes the mass of the rear driveshaft, differential, and axle shafts from the system. The natural vibration frequency of a system depends partially on its mass and the mounts. If the natural frequency is the same as the frequency that it's being "excited" (pulsed) at, the vibrations don't damp out and average to zero. They grow and grow until they annoy you.

10 Hz just happens to be the same as 600 RPM, the usual warmed-up idle speed. :wink: You can also reduce the vibration by changing your idle RPM to 750 temporarily, which I did as an experiment with EFILive while I was troubleshooting my own motor mount problem.

Aftermarket motor mounts are not duplicating exactly the OEM units in terms of viscosity and stiffness, which is why they often fail to solve the problem. That's why we always recommend OEM mounts, no matter what the price.

Roadie, is this vibration felt in the pedal? After installation of my ported throttle body, I have a very noticeable pedal/engine vibration at exactly 1000 rpms, it only occurs either in drive from a dead stop or ever so slightly in reverse also at 1000 rpms. Is it possible that the ported throttle body simply shifted the 10hz vibration upwards to 1000 rpms or does this sound like a separate issue to you? Thanks for your input.
 

Aukland

Original poster
Member
Jan 12, 2012
50
My personal experience so far is not the pedal rather the entire vehicle vibrates. But assuming it is the motor mounts it would be a different scenario with a ported tb.
 

The_Roadie

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Pittdawg said:
Roadie, is this vibration felt in the pedal?
As it's a drive-by-wire system (all electronic) there's no traditional cable between the butterfly valve and the pedal, so any pedal vibration has to be coming from the body. Where it's easy to notice is on the intake manifold. Due to the flexibility, it vibrates with a higher amplitude than the exhaust manifold, for instance. Go look.
After installation of my ported throttle body, I have a very noticeable pedal/engine vibration at exactly 1000 rpms, it only occurs either in drive from a dead stop or ever so slightly in reverse also at 1000 rpms. Is it possible that the ported throttle body simply shifted the 10hz vibration upwards to 1000 rpms or does this sound like a separate issue to you? Thanks for your input.
If the vibration goes away if you slap it into neutral when you're rolling with 1000 RPM on the tach, it might be from the same root cause. Or if it vibrates less when warm than cold. Or it could be some other rotating part like an imbalance in the fan blade, loose water pump bearing, etc. I'd put a camera in the engine compartment or remove the hood to take a look from the driver's seat to see if the vibration's amplitude at the intake manifold had a peak at the 1000 RPM (16 Hz) resonant frequency. Or find a local friend and swap throttle bodies for an experiment.
 

Pittdawg

Member
Dec 5, 2011
538
the roadie said:
As it's a drive-by-wire system (all electronic) there's no traditional cable between the butterfly valve and the pedal, so any pedal vibration has to be coming from the body. Where it's easy to notice is on the intake manifold. Due to the flexibility, it vibrates with a higher amplitude than the exhaust manifold, for instance. Go look. If the vibration goes away if you slap it into neutral when you're rolling with 1000 RPM on the tach, it might be from the same root cause. Or if it vibrates less when warm than cold. Or it could be some other rotating part like an imbalance in the fan blade, loose water pump bearing, etc. I'd put a camera in the engine compartment or remove the hood to take a look from the driver's seat to see if the vibration's amplitude at the intake manifold had a peak at the 1000 RPM (16 Hz) resonant frequency. Or find a local friend and swap throttle bodies for an experiment.

It is still present in neutral, possibly less pronounced but still there.
 

Aukland

Original poster
Member
Jan 12, 2012
50
I took it over to my buddy and let him have a look. It was indeed a pass. side motor mount. I will have it fixed hopefully next week. Thanks everyone!
 

Regulator

Member
Nov 20, 2011
2,496
A trip to Indiana and we can take care of it in the driveway. Gas to get here would probably be cheaper then paying a shop!

Sent from my SCH-I510 using Tapatalk
 

Aukland

Original poster
Member
Jan 12, 2012
50
I just gotta pay for parts :smile:. We will do it in the evening after they close shop. But thanks for the offer Matt, much appreciated!
 

Voymom

Member
Feb 3, 2012
2,523
Aukland said:
Very much appreciated. That one will wait till the weekend where i can pull it into a decent area and work from there. RPM's on start up are a bit above 1k then lower as it run's. Didn't know if that also had any relevancy to this matter (could be something entirely different, Maybe a vacuum leak?)

I have an 03 Envoy. Not sure if anyone mentioned but it is normal to have the RPM's a bit above 1k at start up. It should fall down to around 600 RPM's after the engine warms. Mine hits 1500 RPM's then drops to 600 RPM's after about 3-5 minutes.
 

The_Roadie

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Voymom said:
Not sure if anyone mentioned but it is normal to have the RPM's a bit above 1k at start up. It should fall down to around 600 RPM's after the engine warms. Mine hits 1500 RPM's then drops to 600 RPM's after about 3-5 minutes.
I posted the chart of how the PCM manages this in post #10. :wink:

neelskit said:
Does any one know the GM Part Number for the I-6 Mounts?
Motor mounts 15062381; transmission mount 89040448 Don't use aftermarket.
 

Dan

Member
Apr 5, 2012
2
My 2004 6cyl 2wd Envoy XUV also vibrates while idiling in drive. I've changed the throttle body, accelerator pedal w/ sensor, spark plugs, and motor mounts. The check engine light isn't on. One of the mechanics where I work checked it on his expensive diagnostic computer and something came up with the antilock brake system. When I disconnect/reconnect the battery, the engine idles properly for awhile then it starts again. I'm thinking it could be a short or a sensor. Anyone have any idea what's going on?
 

Dan

Member
Apr 5, 2012
2
the roadie said:
How many miles? Did you use Delco 41-103 plugs? Did the mechanic check O2 and MAP sensor data? Compression? Inspect the plug coil packs for evidence of sparking on the boots?

It has 138k miles and I've never changed the O2 or MAP sensor. I don't remember if I used Delco plugs. The mechanic didn't check the compression. Don't remember if he checked the O2 or MAP sensor data. I thought everything was OK mechanically since it runs fine after the computer memory is cleared. Is that not a correct way of interpreting that?
 

The_Roadie

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Nov 19, 2011
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The sensors could have bad data, and the engine runs on different tables when it's first learning the performance after a battery disconnect.

Hmmm, did the motor mounts get changed with aftermarket or with OEM? OEM are the only ones that work well. But that wouldn't explain the getting worse issue.
 

rcroyer85757

Member
Apr 9, 2012
4
Well i have an 03 TB with 117k, having a very similar problem. First off let me give you a timeline and what has been done. Around Christmas of 2010 i noticed that the same would happen (Vibrates in drive at idle, goes away/dramatically less in park or neutral) and I assumed the same that it might be the transmission. I also assumed this because it seem to be worse when the engine was cold and seemed to go away when it heated up. After the transmission fluid was flushed the vibration continued. I put off getting it looked at for a while and over the last year it has been progressively been getting worse. Now in the last month it has gotten ten times worse than it has ever been. That being said we are planning a trip to Disneyland and now I have been focus on getting it fixed. Now to what I have done. First I talked to one mechanic and he suggested looking to see if there were any updates for the computer, and sure enough there was one for "idle in gear". After spending the money on that it seemed to get better, but eventually was back to being as bad as it was. Then I took it to another place and actually got a Diagnosis done. They came back with need fuel system cleaning, new motor/transmission mounts and plugs with boots. Also transmission tails shaft seal was leaking on the transmission mount and wore it out prematurely. I took it to another place and had them look at it, they came to the same conclusion and I had them do it. Vibration was still there so I took it back and they replaced the motor mounts once again and the problem was still there. Before i continue let me say NO they were NOT the OEM plugs and Mounts, BUT before you jump to that as the problem let me continue. In the mean time I noticed another problem. While sitting in park at an idle the tachometer would drop by about 200 rpm and the voltage would drop by about one or two volts. Also on shut down of the engine it would sound like it would diesel, or just shut down hard. After taking it back to the third mechanic He noticed that the fan clutch and the water pump had bad bearings so I had those replace with no improvement. Now on to what I have found, I started with cleaning the throttle body, the correct way (taking it off and cleaning the back and front and disconnecting the battery for more than 30 minutes). Now the rough shut down has gone away. After doing this I took the serpentine belt off and ran the engine for about 2-3minutes and the vibration went away. This tells me that it is something that is belt driven that is making it vibrate. Remember that I do NOT have OEM mounts or plugs, but it did NOT vibrate with the belt off. With the belt off I ran each of the bearings by hand and noticed the power steering pulley would run smooth and every 6-8 revolutions it would get harder to turn. Now at this point I have had the power steering fluid flushed and the oil changed and still have the vibration........ So I guess at this point my question is assuming that the problem is something belt driven and already having the fan clutch and water pump changed what should i be looking for and what should I try next....... Also as for the Disneyland trip (1000 mile round trip), would you say that it would be ok to drive that far if I cant fix this by then?
 

The_Roadie

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rcroyer85757 said:
Vibrates in drive at idle, goes away/dramatically less in park or neutral
Clue #1.
)..worse when the engine was cold and seemed to go away when it heated up.
Huge clue #2.
...NO they were NOT the OEM plugs and Mounts,
Aftermarket mounts are too stiff. Use only OEMs. And only Delco 41-103 plugs.
BUT before you jump to that as the problem
Too late. :wink:
lWhile sitting in park at an idle the tachometer would drop by about 200 rpm and the voltage would drop by about one or two volts.
If this behavior goes away when the AC compressor was turned off it's 99% chance to be a dirty throttle body and the previous work caused a PCM reset that needed to be relearned and a dirty sticky throttle body can't be relearned.
Also on shut down of the engine it would sound like it would diesel, or just shut down hard. After taking it back to the third mechanic He noticed that the fan clutch and the water pump had bad bearings so I had those replace with no improvement. Now on to what I have found, I started with cleaning the throttle body, the correct way (taking it off and cleaning the back and front and disconnecting the battery for more than 30 minutes). Now the rough shut down has gone away.
You discovered this AFTER you wasted all that money on mechanics who don't know how to Google? :eek:
After doing this I took the serpentine belt off and ran the engine for about 2-3minutes and the vibration went away. This tells me that it is something that is belt driven that is making it vibrate.
Oh, maybe you DO have something different.
Remember that I do NOT have OEM mounts or plugs, but it did NOT vibrate with the belt off.
And the mechanics you paid never thought to do this? :confused:
With the belt off I ran each of the bearings by hand and noticed the power steering pulley would run smooth and every 6-8 revolutions it would get harder to turn. Now at this point I have had the power steering fluid flushed and the oil changed and still have the vibration........ So I guess at this point my question is assuming that the problem is something belt driven and already having the fan clutch and water pump changed what should i be looking for and what should I try next....... Also as for the Disneyland trip (1000 mile round trip), would you say that it would be ok to drive that far if I cant fix this by then?
I'd swap the PS pump if the vibration cleared up so dramatically. First time in six years I've read this kind of report, but everything has a first time. I just don't trust the dynamics of aftermarket motor mounts.
 

rcroyer85757

Member
Apr 9, 2012
4
the roadie said:
If this behavior goes away when the AC compressor was turned off it's 99% chance to be a dirty throttle body and the previous work caused a PCM reset that needed to be relearned and a dirty sticky throttle body can't be relearned.

No, actually the problem is there whether or not the A/C is on, like I said it seems to be worse in the mornings, when i generally don't use the A/C. As for relearning, I thought that disconecting the battery for over 30 minutes would do this, but if no is that something the mechanic must do or is there something else to fix the PCM reset?


the roadie said:
You discovered this AFTER you wasted all that money on mechanics who don't know how to Google? :eek:Oh, maybe you DO have something different. And the mechanics you paid never thought to do this? :confused: First time in six years I've read this kind of report, but everything has a first time. .

Ya my thoughts exactly about the mechanics, its so hard now a days to find a good mechanic, I think that I just had a few things that all came together at one time and its trying to diagnose one at a time and get them resolved. Also I forgot to mention in the original post I also have some other symptoms.......

If I roll the windows up (multiple) at the same time when they hit the top limit or when the wheels are straight and I only move the steering wheel about 30 degrees in either direction the tachometer will drop about 200-300 and the voltage will drop about 3-4 volts?
 

Wyle

Member
Dec 4, 2011
200
the roadie said:
rcroyer85757 said:
BUT before you jump to that [non-OEM mounts] as the problem
Too late. :wink:
:rotfl: He didn't get the word in time, but he's now heard firsthand about OEM plugs and mounts (and CPAS and O2) and knew he'd get flack here. :yes:

the roadie said:
rcroyer85757 said:
Also on shut down of the engine it would sound like it would diesel, or just shut down hard. After taking it back to the third mechanic He noticed that the fan clutch and the water pump had bad bearings so I had those replace with no improvement. Now on to what I have found, I started with cleaning the throttle body, the correct way (taking it off and cleaning the back and front and disconnecting the battery for more than 30 minutes). Now the rough shut down has gone away.
You discovered this AFTER you wasted all that money on mechanics who don't know how to Google? :eek:
He discovered it after his father gave him common knowledge from GMTNation, AND a can of TB cleaner as a Christmas present, and now showed him the proper way to use it. :raspberry:

On a positive note, he did help me pull the front axle out of my TB. :thumbsup:

I lifted his hood Sunday and headed straight for the mounts. That might be a small part of his problems, but its more than that. Hands off idle, and sometimes its hard to focus on the electrical connectors above the wheel well. The aluminum crossover AC closes a 3/16" gap and bangs against the intake resonator. Quarter turn of the steering wheel and it drops to ~300 rpm and bucks like mad. I know free spin is a lot different than loaded, high rate spinning, but even by hand, a fairly consistent "hand prop" of the pulley would make it go a full rev, then there'd be a half dozen time where it would only go a quarter rev, then back to full spins again.

And since you didn't make an intro post, I'll say it here ... Welcome to TrailBlazer school, Son. (Next time, start your own thread :hijack: )
 

The_Roadie

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Nov 19, 2011
9,957
Portland, OR
Wyle said:
...and knew he'd get flack here. ...
A few Dads take their sons to Nevada to "make them a man." You throw yours into a forum with the Roadie. Cool. :rotfl: :wootwoot:

Seriously, I've never heard of a PS pump being so bad that it could cause a well-idling engine to stall out or reduce RPMs like that. The voltage dropping is normal for any RPM under 600, though. That's an effect and not a cause. But they're relatively cheap to swap. Just a challenge to swap pulleys from the old to the new.

If the plugs are now Delco 41-103, then check compression as the next suspicious item. And vacuum.
 

rcroyer85757

Member
Apr 9, 2012
4
Well at this point have have some good news.

After cleaning the TB the engine has not shut off hard yet (has been two days now):smile:

After changing the PS pump the random loss of RPM while parked or at idle has stopped.:smile:

Also checked the plugs, they are the Delco's :smile:

Bad news is that the vibration is still there and now is constant in all gears. . At this point I am still befuddled. Without the serpentine belt this thing runs smooth as glass, with the belt there are time when it is so bad I can barely hold on to the steering wheel?
I called the dealer just to get another opinion and he is leaning toward the mounts too :redface: I asked him how much the mounts were and it turns out they were lower than the aftermaket ones :frown:
 

Wyle

Member
Dec 4, 2011
200
rcroyer85757 said:
Well at this point have have some good news.

Wait for it. Wait for it. rcroyer has more news coming. :rotfl:
 

rcroyer85757

Member
Apr 9, 2012
4
Well I have GREAT news...... :wootwoot:The vibration has all but gone away, the car runs as smooth as glass, in fact, you cant even feel the car running........

Yes it WAS the motor mounts......:wink:

At this point you can still feel a little (in the best terms I can put it) wiggle in the engine, but no vibration.
I was able to feel the vibration in the seats and the steering wheel when at an idle and now not even a hint of a vibration.

I explained it to my dad this way, I had a bottle of water in the cup holder and the water in it was splashing all over the sides, now i cant even tell there is water in the bottle......

So to recap

Hard shutdown = dirty throttle body
Random drops in RPM = power steering bearing
Ticking sound = fan clutch
VIBRATION = motor mounts

Thanks everyone for you help :thumbsup:
 

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