Rough idle in drive but only when sitting at a stoplight

[vt_maverick]

So having a bit of a problem that has me concerned. When I'm sitting at a stop sign or light with the transmission in Drive and my foot on the brake, I get a vibration/growling noise about a second after I come to a stop. The noise is constant until I left off the brake, then it goes right away (I don't even have to accelerate). I don't experience this issue anytime else, not while in Park, Neutral, accelerating, decelerating, shifting between gears, etc. I've done a good amount of digging and it seems like all the related threads dealt with issues experienced in those situations. Does anyone have an idea what might be going on? The vibration is very pronounced and can be clearly felt through the brake pedal, bad enough that I usually shift into Park or Neutral at lights just to avoid the aggravation.

Thoughts? Thanks!

[tom4bren]

My first thought would be vacuum leak on the brake booster.

I don't know nuthin 'bout brakes though - I just pulled that one out my arse.

Have you tried to stop a little early, let off the brake & creep forward a little then stop again to see if it still does it.

[vt_maverick]

Yep, I've done that a few times hoping it will "reset" whatever the problem is. Unfortunately that does not work, it happens every time I come to a complete stop with my foot on the brake.

[tom4bren]

Try pulling the ABS fuse to see if it goes away - just trying to eliminate variables.

[etlsport]

also turn off your climate control.. mine behaves exactly like this any time the AC is switched on (heating or cooling), whether the compressor is on or not.

i was actually just starting to wonder about the brake booster after reading your post the first time (couldnt respond from work) so thats my next step to curing the problem.

[vt_maverick]

Already tried turning off the AC with no love, but I'll give it another go on the way home today. Tom I'll give the ABS fuse a try too. Is it in the fuse panel on the left side of the dash, or under the box in the engine bay?

[tom4bren]

Sorry, Ida know

[Bob Barker]

Sounds like a simple vibration from a bolt or nut that occurs at a certain engine RPM. My wife's car does it all the time, and the SVO does it, my old Mach used to do it... Just gotta dig around until you can find the source. I could be way off, but it's the free-est thing to try that may get rid of the noise.

Does it make the noise when the engine is still in it's "warming up" phase, like early morning at the first stop you make, or is it after you have been driving a while and the engine is warmed and set at it's normal RPM while in gear at a stop?

[Bob Barker]

and I'm pretty sure the ABS fuse is under the hood. I think I remember seeing it there.

If it were break booster, I imagine the vibration would get worse if you were to press harder on the brake pedal after you stop. If you are stopped, and the vibration starts, push way down on the brake pedal and see if the vibration gets worse/better/stops/kills the truck. Something will change if it's a vacuum issue with the breaks.

[vt_maverick]

Happens from the moment I start her up until I get wherever I'm going. Seems to be something driven by the "tug of war" between the drivetrain and brake system.

[vt_maverick]

...push way down on the brake pedal and see if the vibration gets worse/better/stops/kills the truck.

That's not exactly comforting Bob. :)

[Bob Barker]

Maybe have someone hold the brake pedal down in the drive way while you listen around under the hood or chassis or wherever the source of noise is.

[Bob Barker]

That's not exactly comforting Bob. :)

:bwgy:

It's not the worse if that happens. It will tell you what the issue is! If the truck kills then it's safe to assume that you used all the available vacuum in the system to press the brake pedal to max, and since it was leaking, you used more than the truck was producing.

:_confused

[Mile High VX]

Maybe have someone hold the brake pedal down in the drive way while you listen around under the hood or chassis or wherever the source of noise is.

Make sure that they like you if you choose this option...:yesgray::yesy::yeso::yesb:

[etlsport]

Mine will not cure right away when I turn off the ac but like earlier today I stopped at a light and had an awful idle. Switched off the ac and nothing happened. I idled forward when the light changed but still missed the light. When I stopped it was idling perfect

[Marlin]

If it is pronounced through the brakes, I too would tend to lean toward ABS, but then the light would be on. The fuse is under the hood, clearly labeled on the fuse diagram. That will have no effect on your vehicle other than no ABS and light on in the dash display. I pulled my fuse long ago...

[vt_maverick]

Which fuse is it? Looks like there are 2, one a 20A and the other a 40A:

http://www.vehicross.info/gallery/data/3269/medium/IMG00180-20101123-1637.jpg

[tom4bren]

If it is pronounced through the brakes, I too would tend to lean toward ABS, but then the light would be on. The fuse is under the hood, clearly labeled on the fuse diagram. That will have no effect on your vehicle other than no ABS and light on in the dash display. I pulled my fuse long ago...

I was just thinking that if the ABS is 'confused' it may try pulsing the system whilst at a full stop, causing the vibration. It's a long shot but easy to check out by just pulling the fuse.

[RickOKC]

Hmmm, I wonder if this was my mystery sound. Soon after I got my VX, I noticed a very low frequency sound/vibration when I was in gear with the brakes on. In fact, it reminded me of the sound brakes can make sometimes when you creep forward. Maybe it was the last dying gasp of the ABS. It took a few days but the mystery sound eventually disappeared.

[vt_maverick]

It's a long shot but easy to check out by just pulling the fuse.

That's great, but which of the two fuses is it (see question above)? ;)

[circmand]

That's great, but which of the two fuses is it (see question above)? ;)

pull them both or pull one then the other either way it tests the proposed problem. Have you given considerationof stopping by a brake place and letting someone wo can see and hear the problem make a suggestion? After all diagnosis by description is quite difficult . BTW dont rely on not seeing the light it may be burnt out.

[etlsport]

You can also try pulling the e brake while topped and releasing the regular brakes to see if that makes a difference. mine was plenty strong to hold me in place. Alas didn't do a thing for my rough idle though

[vt_maverick]

Just trying to do a little pre-diagnosis so I can determine if I need to start working on finding parts. I'm really not a big fan of being out of a car for a day only to hear that they couldn't get the part they need so I've got to go back, order it through Isuzu, then repeat the process again next week. The research paid off with the neutral safety switch issue, so I was just thinking the same way here.

We're going to be out of town for the holiday but I believe my garage is open Friday. I might drop off the VX Wednesday afternoon and let them keep it through Saturday since it doesn't impact my commute or anything.

[vt_maverick]

also turn off your climate control.. mine behaves exactly like this any time the AC is switched on (heating or cooling), whether the compressor is on or not.

i was actually just starting to wonder about the brake booster after reading your post the first time (couldnt respond from work) so thats my next step to curing the problem.

You know I tried turning off climate control on the way home, and it did seem to help. I'm going to test that theory more tomorrow morning before I pull the fuses. Figure I can get a baseline for climate control off but ABS (fuse anyway) on, then test climate on/off with the fuse pulled.

If it is HVAC related, anybody got a suggestion? It's a vacuum issue then I guess?

[vt_maverick]

what does it matter... pull them both or pull one then the other either way it tests the proposed problem.

It matters (to me at least) because I don't understand what the ramifications of pulling them independently or together would be under normal circumstances, let alone when something is wrong. Disabling parts of your brake system just to see what happens without understanding what you're doing sounds like a recipe for disaster to me.

[Marlin]

It matters (to me at least) because I don't understand what the ramifications of pulling them independently or together would be under normal circumstances, let alone when something is wrong. Disabling parts of your brake system just to see what happens without understanding what you're doing sounds like a recipe for disaster to me.

ABS is a stand alone system and not part of the brakes in the manner your thinking. Feel free to pull the ABS fuses, no worries, your brakes will still work just fine. Smiley and I have have been that way for a long time, and I am sure that there are others. If you don't like it, or it doesn't help, just put em back in.

[Ldub]

Happens from the moment I start her up until I get wherever I'm going. Seems to be something driven by the "tug of war" between the drivetrain and brake system.

Same symptom here...been that way since I bought her off the used car lot...:_confused

Thought I had a handle on it once when I diddled with the trans mount, but no bueno'.

Finally resigned myself to the fact that it's just a "normal" VX noise...if it's anything that's gonna break, that's when I'll fix it...:_wrench:

[VX KAT]

Hmmmm, vibration/growling sound.....could it be what I'm having??...where something along the exhaust system is touching the Kilby skid plates? Mine rattles and growls when in Drive, and brakes applied at a stop.

It developed during my road trip. Jack and Dub both pushed/pulled on the muffler and some other exhaust pipes and it stopped. *Of course it's hot so be careful when you grab around there.*

I haven't had it evaluated yet.

[deermagnet]

I just Googled 'rough idle in drive when stopped'. There's a ton of stuff for this problem. It's mostly just shots in the dark, but motor and tranny mounts are frequently mentioned. Give Google a try and see if some of the possible causes might be applicable to your VX.

Mark

[vt_maverick]

Hmmmm, vibration/growling sound.....could it be what I'm having??...where something along the exhaust system is touching the Kilby skid plates? Mine rattles and growls when in Drive, and brakes applied at a stop.

Could very well be. Maybe I'll crawl under the VX and take a picture of the top (inward facing) side of the plates to see if there's any shavings or scratch marks. That's a pretty scary thought. Maybe if I drop it off at the mechanic tomorrow afternoon I'll get an answer for you guys.

And thanks for the reassurances Marlin and Dub, I'll pull those fuses tomorrow and see what happens.

[Ldub]

Hmmmm, vibration/growling sound.....could it be what I'm having??...where something along the exhaust system is touching the Kilby skid plates? Mine rattles and growls when in Drive, and brakes applied at a stop.

It developed during my road trip. Jack and Dub both pushed/pulled on the muffler and some other exhaust pipes and it stopped. *Of course it's hot so be careful when you grab around there.*

I haven't had it evaluated yet.

Been under there with my own eyeballs, your problem is that the pas side (IIRC) exhaust makes contact with the kirbys...maybe a few washers between the frame & the skid plates would work?:_thinking

[Marlin]

You said it was a grinding rubbing sound you could feel through the brakes. That is not the same as a rattle/vibration. There are so many heat shields on our exhaust, I have methodically removed them as they start to rattle. I have one left, and I had to remove the one above the transfer case as well. No more rattles:)
Mine only rattle when the brakes are on and I am sitting. That is your problem...a fast tink tink tink sound. Very annoying, but doesn't hurt anything, put it in neutral or start moving and it goes away.

[vt_maverick]

Update... I shut off the A/C on the way to work this morning and had no problems. Flipped it on at the stoplight just before our parking lot and the sound came right back. So does that change the diagnosis? I haven't pulled the ABS fuse yet, probably do that on the way home.

[tom4bren]

That's great, but which of the two fuses is it (see question above)? ;)

"Quit changin the subject and answer the fookin question"

My favorite quote from Braveheart - ya gotta say it with a heavy Scottish accent.:)

[Bob Barker]

Update... I shut off the A/C on the way to work this morning and had no problems. Flipped it on at the stoplight just before our parking lot and the sound came right back. So does that change the diagnosis? I haven't pulled the ABS fuse yet, probably do that on the way home.

That makes me think it's a vibration somewhere. If the load on the engine changes and makes the noise come and go then I immediately think vibration. It's still a free check to pull the ABS fuses and then test for vibrations with/without a/c.

[circmand]

It matters (to me at least) because I don't understand what the ramifications of pulling them independently or together would be under normal circumstances, let alone when something is wrong. Disabling parts of your brake system just to see what happens without understanding what you're doing sounds like a recipe for disaster to me.

while the systems are seperate I did not mean to suggest pull them and go out on the road drive just pull then a brief driveway idle test to see if the problems still exists.

by the way have you greased your drive train lately. Not sure if it would cause this but it might.

[vt_maverick]

UPDATE: While the shop was trying to find the electrical gremlins in my fog lamp, I asked them to also track down the source of the vibration. Apparently it's being caused by the exhaust pipe rattling against the Kilby skid plate, so they checked all the hangers and found that everything was tucked up tight like it should be. They told me that there's like a 1mm clearance between the pipe and the plate at off/idle/park, but that the slight vibration associated with being in drive is causing it to contact. It's probably happening at speed too, but it's more noticeable when you're sitting still. They suggested cutting a hole in the plate to eliminate the rub, which I thought was a good idea given this problem and the concerns that Sue, I, and others have had with the potential for significant heat build-up with the Kilby plates. I'll take a pic when I get it back so you guys can see what was done.

Can't wait to pick it up to see how much better it drives/stops!

[Marlin]

Didn't need a mechanic to figure that out, see post #32...You gotta get down on the ground and get dirty, get to know your VX, be at one with her. Stop paying a stranger to feel her up on simple things:bgwb:

[VX KAT]

UPDATE: Apparently it's being caused by the exhaust pipe rattling against the Kilby skid plate, so they checked all the hangers and found that everything was tucked up tight like it should be. They told me that there's like a 1mm clearance between the pipe and the plate at off/idle/park, but that the slight vibration associated with being in drive is causing it to contact. It's probably happening at speed too, but it's more noticeable when you're sitting still. They suggested cutting a hole in the plate to eliminate the rub, which I thought was a good idea given this problem and the concerns that Sue, I, and others have had with the potential for significant heat build-up with the Kilby plates. I'll take a pic when I get it back so you guys can see what was done.

Can't wait to pick it up to see how much better it drives/stops!

I just had mine finally addressed last week....exhaust touching the Kilby's...so he tightened up the hanger some how a small amount. Said it will eventually return as the hanger loosens, but you don't want to put the exhaust up any higher, closer to undercarriage. I'm fine with that. Will address any cutting/venting issues later. Jack, Dub and RallyDude all suggested a backward facing cupped shape chunk of metal be welded over any hole we cut.

[vt_maverick]

Didn't need a mechanic to figure that out, see post #32...You gotta get down on the ground and get dirty, get to know your VX, be at one with her. Stop paying a stranger to feel her up on simple things:bgwb:

Actually I'm paying them to fix the problem since I don't have the tools to make the cuts myself. It's also not exactly easy to reinstall the Kilby plates by yourself and without it up on a lift - when Tom and I installed them we had to take turns holding the plates while the other bolted them down because they were so heavy.

Oil changes, bulbs, general troubleshooting, no problem.

[Marlin]

Actually I'm paying them to fix the problem since I don't have the tools to make the cuts myself. It's also not exactly easy to reinstall the Kilby plates by yourself and without it up on a lift - when Tom and I installed them we had to take turns holding the plates while the other bolted them down because they were so heavy.

Oil changes, bulbs, general troubleshooting, no problem.

I can imagine they are fairly bulky, its a PITA to get the front diff in as well. But a floor jack and 2x4 would make the plates no problem. As for cutting the steel. That is easy, 10 bucks at Harbor Freight gets you an angle grinder, then you can cut whatever you want:) Bwa ha ha ha ha ha ha ha ha ha!!!!! After that, there is no going back....come to the dark side.

[vt_maverick]

Well got her back a few hours ago and the problem is definitely fixed. Long term I'll need to figure out the patch solution mentioned above, but for now I'm very happy to have the smooth ride back. :D