Never ending rough idle....please help

[blackout51]

Here is a list of what I have done so far:
- air filter
- cleaned throttle body
- new engine and transmission mounts
- new o2 sensors
- new auxilary air valve
- new cam timing solenoid
- battery and alternator tested perfect
- replaced two coils that were corroded, the rest look good
- new ac delco plugs
- new thermostat
- new pulley on tensioner (all other pullies sound fine)
- new belt
- new water pump (fan still works like normal)
- transmission fluid changed

I have no idea what it could be, it idles like its misfiring but no codes are thrown and when I let my foot off the brake it surges forward but the rpms stay steady at 625. And any rpm above 625 the truck runs great, no issues at all, it is just at idle and when rolling forwards. I also notice a tapping noise similar to when the transmission shifts but its a continuous tapping in unison with the surges. Something I have noticed is that it ran for a while with low power steering fluid and the pump makes a buzzing noise when running now. Any ideas are appreciated

 

[ItsOnVoy]

Try some simple injector cleaner, that's all that works on my truck when it it does that.

 

[blackout51]

Try some simple injector cleaner, that's all that works on my truck when it it does that.

I forgot to mention that, I ran maybe 5-6 bottles of Lucas injector cleaner and sea foamed the gas as well as the vacuum line twice, all at different tank fulls of course

 

[The_Roadie]

Welcome!

Can you see the roughness by a vibrating radio antenna? If you look closely at the intake manifold where the PCM mounts does it vibrate more than the intake resonator at the top of the engine? Do the mounting bolts for the PCM look fuzzy because they're vibrating like a bumblebee's wings?

Did you use OEM motor mounts? Could they have been aftermarket? Does the vibration change behavior in NEUTRAL instead of DRIVE? Is it at all temperature sensitive?

If the answers are all no, then it might be a deteriorating item like the PS pump or alternator. Remove the serpentine belt and you can run the engine for a few minutes when cold. See if the roughness goes away then. If it does, then you have a problem with a rotating part - unbalanced fan blade assy, water pump, AC compressor bearing, PS pump, alternator, idler pulley, tensioner pulley, bad belt. I know you changed some of these already - this list is for folks who might find this post much later.

Does the behavior change if the AC is forced off?

 

[blackout51]

Welcome!

Can you see the roughness by a vibrating radio antenna? If you look closely at the intake manifold where the PCM mounts does it vibrate more than the intake resonator at the top of the engine? Do the mounting bolts for the PCM look fuzzy because they're vibrating like a bumblebee's wings?

Did you use OEM motor mounts? Could they have been aftermarket? Does the vibration change behavior in NEUTRAL instead of DRIVE? Is it at all temperature sensitive?

If the answers are all no, then it might be a deteriorating item like the PS pump or alternator. Remove the serpentine belt and you can run the engine for a few minutes when cold. See if the roughness goes away then. If it does, then you have a problem with a rotating part - unbalanced fan blade assy, water pump, AC compressor bearing, PS pump, alternator, idler pulley, tensioner pulley, bad belt. I know you changed some of these already - this list is for folks who might find this post much later.

Does the behavior change if the AC is forced off?

Ok some of that I will check tomorrow when i can see, but yes it shook the antenna pretty bad, at the end it had over an inch deviation, so I got a short antenna because it was bugging me so much. The rough idle seems to fade but come right back when I shift from drive into neutral. The motor mounts were dea oem style ones. The alternator does squeak when I turn the pulley but it tested fine so I don't know about that, the power steering pump I am still examining, it doesn't seem like it has leaked since I put the new fluid in but could it really cause. Rough idle? It really only idles rough when it is at 625 rpm, it never goes lower but any higher and it goes away. The A/C doesn't have any effect on the idle, it is the same on or off. The idler pulley spun with no noise or roughness. I'll check the belt off method and the shaking of the bolts on the pcm tomorrow and get back to you.

 

[The_Roadie]

The motor mounts were dea oem style ones.

That's the problem. I haven't heard of an aftermarket mount that's exactly viscous enough to damp the harmonic rotational oscillation at 10 Hz that is the root cause of this problem. Collapsed OEM mounts are too stiff, and the vibration happens. Aftermarket ones are also too stiff. Use OEMs. We discovered this 4-5 years ago on trailvoy. You might be able to prove it by using a prybar under the passenger side mount bracket and take some weight off it. See if the behavior changes. That trick works with collapsed OEM mounts - not sure about the internal structure of the DEAs. Alternatively you can get a PCM tune that will change your idle to 725-750 RPM and solve it a different way. I did that to mine using EFILive while I waited for the time to change my mounts. Unless you invest a bunch ($500+) in the software, you won't be able to fiddle with your own idle RPM.

 

[blackout51]

That's the problem. I haven't heard of an aftermarket mount that's exactly viscous enough to damp the harmonic rotational oscillation at 10 Hz that is the root cause of this problem. Collapsed OEM mounts are too stiff, and the vibration happens. Aftermarket ones are also too stiff. Use OEMs. We discovered this 4-5 years ago on trailvoy. You might be able to prove it by using a prybar under the passenger side mount bracket and take some weight off it. See if the behavior changes. That trick works with collapsed OEM mounts - not sure about the internal structure of the DEAs. Alternatively you can get a PCM tune that will change your idle to 725-750 RPM and solve it a different way. I did that to mine using EFILive while I waited for the time to change my mounts. Unless you invest a bunch ($500+) in the software, you won't be able to fiddle with your own idle RPM.

The old ones were collapsed about an inch but the one on the drivers side felt solid where the new ones as well as the old passenger side one felt fluid filled but the old passenger one felt more then just fluid filled, it was more like something was loose inside it. Should the new ones feel solid like the old drivers side or like the way I described the new ones feel? You think that even though it goes away in neutral that the mounts are still a major possibility?

 

[The_Roadie]

Rough idle in drive that goes away in neutral is THE definitive proof that it's motor mounts.

 

[blackout51]

Rough idle in drive that goes away in neutral is THE definitive proof that it's motor mounts.

Sorry I typed that wrong, it goes away for just a second when shifted into neutral but continues to idle rough even in neutral or park

 

[The_Roadie]

I'm still suspicious of the aftermarket mounts. Try the crowbar trick.

 

[blackout51]

I'm still suspicious of the aftermarket mounts. Try the crowbar trick.

i will still try that when I get home in about 30 min, but one other thing I notice when I'm sitting still idling there is a tapping noise that sounds like its coming from under the truck but I'm not 100%. it sounds similar to tapping a socket on the block, and seems to coincide with the idle

 

[blackout51]

I'm still suspicious of the aftermarket mounts. Try the crowbar trick.

Well from what I checked the crowbar didn't do anything but ill keep in mind that switching them to oem mounts are something ill need to do soon. Also the bolts attaching the pcm to the manifold weren't shaking violently. I didn't have time to pull the belt off though. That tapping concerns me, I don't know what it could be from, it doesn't sound like it coming from the motor, the timing chain sounds fine and there aren't any unusual noises from the engine bay.

 

[gmcman]

Can you post a vacuum reading? Needle steady or fluctuating, in/Hg value?

 

[blackout51]

Can you post a vacuum reading? Needle steady or fluctuating, in/Hg value?

I haven't gotten one done, is there a way I could do this at home rather then a shop?

 

[gmcman]

You can find a vacuum gauge at pretty much any parts store, I would opt for the larger gauge for a few extra $$$. These are invaluable tools and can readily let you know of any valves not completely closing or even a vacuum leak.

There is a small vacuum line near the intake silencer, can't think of the location off the top of my head. Use a "T" fitting and cap the other end so you can still keep the line connected.

 

[CaptainXL]

Did you just buy this truck? You said you changed the air filter. Was it really nasty and black like it never was changed before? Considering what I am going through with my vehicle I know from reading posts on the OS and other sites that a rough idle can be caused by low compression in some (if not all) of the cylinders. This is especially the case if the fuel and ignition systems are ok. Suspect poor maintenance on part of the original owner and check compression.

 

[blackout51]

Did you just buy this truck? You said you changed the air filter. Was it really nasty and black like it never was changed before? Considering what I am going through with my vehicle I know from reading posts on the OS and other sites that a rough idle can be caused by low compression in some (if not all) of the cylinders. This is especially the case if the fuel and ignition systems are ok. Suspect poor maintenance on part of the original owner and check compression.

I got it about 2 months ago, it wasn't black like it had never been changed before but it was pretty bad, and when I cleaned the throttle body it was gunned up but not as bad as my moms envoy when I did hers and it has 40k less miles. I'll try and get a compression test done today

 

[blackout51]

Something else I noticed since its been colder out is that the amount of exhaust coming from the tailpipe seems really small compared to other cars I have had, it's almost like there's barely any coming out, now I know my muffler is leaking and it tried to patch it until I can get a new muffler but the leaks weren't that bad, could something causing this also have something to do with my idle and lurching

 

[Menthol]

Something else I noticed since its been colder out is that the amount of exhaust coming from the tailpipe seems really small compared to other cars I have had, it's almost like there's barely any coming out, now I know my muffler is leaking and it tried to patch it until I can get a new muffler but the leaks weren't that bad, could something causing this also have something to do with my idle and lurching

Blocked Cat? Can you remove the front 02 sensor and see if that helps.

 

[blackout51]

Blocked Cat? Can you remove the front 02 sensor and see if that helps.

I'll try that tomorrow, where can I get a exhaust pressure test done just to be sure?

 

[CaptainXL]

I'll try that tomorrow, where can I get a exhaust pressure test done just to be sure?

Any reputable exhaust shop should be able to do it. Did the test myself buying a cheap gauge on Amazon for about $25.

Honestly though, if you can reach 6K rpm's on the highway I wouldn't be suspecting the CAT. Look on youtube and you will see what negative effects a clogged cat will do to acceleration/rpm's. The symptoms of low power and low rpm are unmistakeable. These CATs are high flow and rarely a cause for concern unless the engine was misfiring and the CEL was flashing for a while.

 

[blackout51]

Any reputable exhaust shop should be able to do it. Did the test myself buying a cheap gauge on Amazon for about $25.

Honestly though, if you can reach 6K rpm's on the highway I wouldn't be suspecting the CAT. Look on youtube and you will see what negative effects a clogged cat will do to acceleration/rpm's. The symptoms of low power and low rpm are unmistakeable. These CATs are high flow and rarely a cause for concern unless the engine was misfiring and the CEL was flashing for a while.

Well it was idling a little rough when I first had it and then I did quite a bit of seafoam to clean it figuring that would help but really seemed to make it worse, it was so much that it killed the plugs and I didn't know I killed them at first and did have to drive home (5 min) with cel flashing because of the misfire from the plugs so I know that did nothing good but it seems to run good and when I get on it I've gotten the rpms up to 5500 but never tried to get 6000

 

[blackout51]

Well I did some investigating today and discovered that there's a tapping/ticking sound coming from the left side of the motor near the valve cover. Not sure if its something with a valve or timing chain or what but when I was watching it idle the motor would shake normally then it would sort of shudder and do what it does when there's a misfire ( deeper shake). I'm not sure what any of this means and will be looking around to do a compression test sometime thus week hopefully, another thing to note is that when turning the steering wheel now it makes a noise similair to vinyl rubbing together but it's just a weird noise it's never made before

 

[gboos]

If the CAT is closed you would have no regular power in all situations and not just a "shaky" idle. CAT can not be the issue.

 

[blackout51]

If the CAT is closed you would have no regular power in all situations and not just a "shaky" idle. CAT can not be the issue.

ok well that rules the cat out because it definitely has power and drives normal its just this stupid idle, and now I'm getting a low frequency noise and vibration sometimes that goes and comes

- - - Updated - - -

If the CAT is closed you would have no regular power in all situations and not just a "shaky" idle. CAT can not be the issue.

ok well that rules the cat out because it definitely has power and drives normal its just this stupid idle, and now I'm getting a low frequency noise and vibration sometimes that goes and comes

 

[awer25]

Well I did some investigating today and discovered that there's a tapping/ticking sound coming from the left side of the motor near the valve cover. Not sure if its something with a valve or timing chain or what but when I was watching it idle the motor would shake normally then it would sort of shudder and do what it does when there's a misfire ( deeper shake). I'm not sure what any of this means and will be looking around to do a compression test sometime thus week hopefully, another thing to note is that when turning the steering wheel now it makes a noise similair to vinyl rubbing together but it's just a weird noise it's never made before

Did you ever find a fix? I'm having what sounds like the exact same issue with my '05 Rainier and the ideas in this thread are helpful, but I'd like to hear what it was for you.

 

[Mooseman]

On a 3 year old thread where the OP hasn't been on for over 2 years, I seriously doubt you'll get an answer. You'd be better off starting your own new thread.