Rough Idle, Vibration, Starting Problem

[PeterJr]

Hello all,

I have a 2005 Silverado 2500HD Regular Cab W/T. I have been having issues with this truck for quite some time now.

Right now I am writing because of a problem with a rough idle that has been getting worse the past week or so. When I come to a stop at a red light or a stop sign the truck can get an extremely rough idle and almost seem as though it is going to bog out / stall.

Sometimes I have to throw it in neutral and give it some gas until the light turns green and I can start moving again.

Another problem I am having is with starting the truck. Sometimes I turn the key and the truck starts fine. About 50 - 75% of the time when I turn the key it will start to crank but will fail after a second. I can then try again and it will usually start up again no problem.

Another problem I am having is with a vibration when traveling at 35 mph and an ongoing vibration starting at about 20 mph - 70mph. The vibration at 35mph is more of a shake / rumble strip vibration almost like there is bubble in the tire. The second vibration is more of a "humming" and I suspect a wheel bearing or cv axle.

Some more information:

Just last week the message center pulled a message: "Battery Not Charging" and was falling below 14 volts.

I just replaced the MAP sensor thinking that would fix the idle but this did not work.

Replaced spark plugs about a month ago.

Changed out diff fluid

Changed out transmission fluid (Full flush & filter)

Changed out oil

Ran seafoam through engine

Ran fuel system cleaner through gas tank

So to summarize:

1. Problem with rough idle at stop sign / red light. Very rough idle - almost stalling out

- Possible fuel filter, fuel pump, spark plugs?

2. Problem with crank / starting. Will not start on first key turn... takes a second try to get the engine to turn over.

- Possible fuel pump, fuel filter, battery, alternator?

3. Vibration at 35mph (Rumble Strip, speed bump vibration / shake)

- Wheel Bearing, CV Axle?

4. Humming from ~20mph - 70mph (Very loud around 50 mph when letting off of gas and cruising)

- Wheel bearing, CV Axle, Tires?

I posted a video of the humming and problem starting at :

Thanks for all of your help,

Peter

[davester]

3. vibration could also be u-joints.

 

As for the idle, I would check that you are getting good fuel pressure (about 60 psi, should say pretty constant at idle and should only drop for a moment, then return to 60 psi when you hit the gas). As well, make sure the bolts on the exhaust manifolds are all there.

 

Maybe see if you can get any codes from the engine computer? Just because the CEL is off, doesn't mean there no codes.

[Motor City Rick]

Are the idle rpm's below 800 rpm's when you think it's gonna stall???

 

Watch the tach to see if the rpm's change when you turn the AC on and off. If it drops and doesn't increase rpm's, start looking at Idle Air Control (IAC) on the throttle body for not functioning properly. It will give hard start / stall if the IAC is completely closed

 

As for the vibration diagnostics, place rear axle on two jack stands. Place truck into drive slowly spin both tires up the speed range to 70 mph (check engine light will go on)

Note when vibration occurs. Tire / wheel balance issues will be 40 to 45 mph then get worse at above 65 to 70 mph.

Observe any lateral run out and tire eccentricity on both wheels The tire / wheels should not have more than .125 inches or I/8 inches in any direction. If so, replace the tire or wheels as required. Vibration at stated speeds, balance wheel assembly's.

 

Now remove both rear wheels, reinstall one lug nut to secure rotor or brake drum. Run truck up a second time, looking at drive shaft run out. If more than .125 or 1/8 inch, replace drive shaft. If vibration is present at any speed while in gear, remove drive shaft and send to a specialize shop for balancing. The majority of drive shafts need balancing from the get go.

 

If the vibration is present in neutral up to 3,000 rpm's it's a motor performance / motor mount / balance issue.

 

Now raise the front end, inspect for looseness / slop in the front end, if found, replace the loose part. Remove front wheels and install on rear. Spin wheels slowly up to 70 mph. Note vibration speeds, if they vibrate above 40 mph, its a balance issue. Look also for any type of run out. As stated earlier, if these wheels have the same issues, replace tire or wheels if run out is excessive.

 

These procedures separate a wheel /tire issue or a chassis issue.

[Raptordude]

Your rough idle could be any number of problems, you need a good code reader to properly diagnose, otherwise you'll be throwing money in the toilet trying to diagnose

 

 

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[Motor City Rick]

Another area is the EGR partially stuck open at idle (which should not be open).

[PeterJr]

Just an update on this:

 

- The rough idle was due to an upsteam o2 sensor that needed to be replaced. Because I got them cheap enough I just replaced both of the upstreams. I think the CAT may be getting clogged / carbon build up because it is starting to happen again subtly.

 

- The starting problem was actually the starter (Go Figure) I replaced it with a new one and it is starting up fine.

 

- The humming problem was fixed with a new wheel bearing. I went with a Timken Hub Assembly & Bearing. (It was the passenger side bearing)

 

I am still having vibration issues and I think it is due to a rear differential / axle issue and am in the process of getting and replacing the whole rear assembly. I also have a Transfer Case leak and am in the same process with that now as well. I have that stuff posted on another thread that you can follow and chime in on here: http://www.gm-trucks.com/forums/topic/204842-transfer-case-rear-differential-issues/

 

Thanks for the help everyone!

[Raptordude]

Glad you got most of it sorted out. Your transfer case leak could be due to the "pump rub" issue I think. I could be wrong, I have a 2wd so not super familiar with the 4x4 components

 

 

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