Ok well I have had my 03 Silverado SS for about 4 months. I bought it used with 9,000 miles on it. Since a few days after I have owned it it has had a stumbling at idle issue were you can feel it shaking the truck. Its not a lope like a cam because it isnt a constant pattern. It comes and goes in intensity and only does it when the truck is hot(coolant temp at 210). It has been to the dealership probably 10 times in the last 4 months and after much going back and forth and having a Area Service Manager from GM come out they say it is normal. Their reasoning for it being normal is they had a 05 Silverado SS on the lot that they checked that supposidly did the same thing. According to the guys at the dealer ship this is a 6.0 liter issue. I have a friend with a 05 SS and he does not have this problem. Anyone else experience this kind of problem?

The truck has zero misfires, they replaced the intake manifold gasket thinking it may have been the problem but it wasnt, the truck is 100% bone stock, I only run 93 octane gas in the truck, plugs and wires were changed with no effect.

I have hooked it up to a scan tool and the L-Trims usually float around 5 or 6 on both banks and goes up to 10 or 12 at times. Anyone know what the L-Trims are suppose to be on say a Silverado SS at idle or anybody with a VHO?

Im at a loss for how to fix this. GMs position is that its not a problem but its annoying as hell. It just doesnt seem right that a vehicle that costs almost $40K would have this problem. I kind of get the vibe from the service people that they just want me to go away. Im going to pick my truck up today from the dealership and sit in this Silverado SS the dealer has on the lot to see if it does the same thing. If all else fails I might drive my buddies SS up to the dealer to show them that its not normal.

 

I have the same thing with both my 04 GMC ECSB 5.3 and my 06 Silverado Z71 ECSB L33 HO 5.3

I had my tuner on the Z71 just up the Idle RPM's about 25 RPM and it took care of it.

 

If it is an intermittent bump/roughness that you can feel in the steering wheel when in drive, then it is more than likely a spark plug. I know you said the plugs & wires were replaced, but hear me out. Until recently I worked for an automotive repair chain for many years. Our specialty was driveability diagnosis, and in the last few years I have seen a dozen or more 5.3, 5.7, and/or 6.0 liter Vortecs with a bump in the idle when warmed up. The platinum and iridium plugs can cause this with NO MISSFIRE codes. Switch to Bosch Super Part # 7704 ( HR9LCY ). The platinum/iridium plugs have the very very tiny positive electrode and they are prone ( in certain applications ) to spark deflection/scatter at idle when warmed up. The smallest particle of carbon or deposit from gasoline additive packages on the edge of the positive electrode can cause this condition.

 

My 05' Silverado VHO (6.0L, LQ9) does the same thing. Your going to just have to deal with it. Mine does it, but it's not all that bad or anything.
Try what Allen Nelson (FARM-TRUCK) said above about the spark plugs if it totally gets on your nerves. What are you doing idling for so long anyways??
These things love to be driven and flogged!

Jim

 

...Back when I was stock, mine idled fine and purred like a kitten. I wouldn't hesitate to bump the idle up a little either. Did you happen to look at the TB and see if there was any home porting or polishing done?

 

Sitting in traffic. Up here in Chicago we get alot of it.

When I changed the plugs and wires I went with MSD wires and NGK TR55 plugs but it didnt help.

The throttle body is untouched.

Im going to see about having it tuned and maybe bumping up the idle a bit to see if it smooths it out.

I went to the dealership yesterday and the 05 SS they had, had the same problem as mine so I guess it is a common problem but I still think its complete bullshit that GM thinks its ok for a vehicle this expensive to do that.

 

Check your fuel pressure. Sounds to me like it may have a bad fuel pressure regulator.

 

I think they replaced the fuel pressure regulator I need to check my paper work. I know they replaced the fuel filter.

 

on my LQ9 i dont have any issues with stumbling but im not stock either

 

mine was doing the same thing, i just raised the idle 50rpm's and it's fixed.