Gm V8 shaking in idle

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Apr 6, 2004
PEI, Canada
I have '14 Tahoe with 5.3L. Whenever I come to stop after driving, the engine doesn't idle smooth. Well, it does, for about 20 seconds. Silky smooth. After that, I can feel a faint shake through the floor. Before you say you don't feel it in your truck, put your left knee against the door trim while the engine is idling. Or look at the water in your plastic bottle in the cupholder.
The throttle body, MAF sensor and the engine's insides overall are clean. I wiped the intake pretty good through the TB opening while cleaning it. Smoked the engine multiple times through vacuum booster, no air leaks. I have AFM disabled through the stock tune (the only thing that is changed in the parameters). And there is a two-stage (sequential) catch can on the dirty driver's side.
I've been in several 5.3 trucks, and they all felt pretty much the same. Even the new gen DI engines have that faint shake.
So what is it? Why the engine is smooth for a while, and then shakes all of a sudden, and runs like that thereafter in idle?
How much mileage do you have on the upstream oxygen sensor(s) ?

I have the exact same problem and have been thinking of changing the upstream oh-two.
My 2014 Silverado does the same thing BUT only on 87. If I have E85 in the tank she is silky smooth at idle.

Idling in park I don't notice it as much. Idling at a stop light with my foot on the brake is when I notice it most.
Does the shakiness change if you stop at a light and then put it in neutral? Could be motor mounts. Not necessarily bad motor mounts, just they might not be designed to make it so smooth you can balance a penny on the engine.
Find someone with an advanced code reader ( that can display real time data ) and that knows how to use it .

How are the spark plugs and the rest of the ignition system ?

Best of luck to you , :)
My '13 Avalanche does the exact same thing. As did my old Silverado 5.3. Seems to be a common issue. I think it comes with the ownership of a GM 5.3.
It's an emissions thing. They have to run them really lean at idle for smog reasons or so I was told. Had a 6.0L vortec that did it since new. The Drive-Thru was really annoying in that thing. Hate on Modular Fords all you want they are some smooth running motors.
Originally Posted By: 2strokeNorthstar
It's an emissions thing. They have to run them really lean at idle for smog reasons or so I was told. Had a 6.0L vortec that did it since new. The Drive-Thru was really annoying in that thing. Hate on Modular Fords all you want they are some smooth running motors.

I always thought that an engine idling smoothy is an engine that's burning cleanly. No missfires.
Ok. Oxygen sensors are original, that makes it three years, pretty much brand new.
No E85 available here in Ontario where I am. Tried Shell 97, no ethanol, the truck didn't see the difference at all. Still shakes in idle.
Putting it in neutral doesn't make huge difference. Still shakes. Checked motor mounts for the torque twist, all solid.
I'very got Tech2,not sure what is more advanced reader there is... I didn't see anything out of order regarding fuel trim or air, idle or driving.
IAC- can't be sticky throttle plate, as I cleaned everything pretty good, including the shaft. It didn't make a difference anyway.
Gotta check actual injector timing when it starts happening. If they trim it significantly after idling for a while, will talk to Diablo to make some adjustments to the stock tune... I bet they know about the issue anyway...
I conclude that GM is doing it for emissions, as most owners would not notice that faint shake anyway. If I find a solution, I'll post it here.
Shell 97 with no ethanol? I'm moving to Canada!

This really seems to be a GM V8 thing. Got 3 NPR HDs with LS based engines, and the vibe is something they just do. Never thought about it, because they have a job to do, and I could care less about NVH, but it's something I might start investigating for the H of it.

On the other hand, I've had and come across a lot of silky big blocks.
For what it may or may not be worth , the company 2008 Chevy Silverado , I think has the 4.8l LS engine . 160,000 miles , still has the OEM spark plugs . Purrs along at idle , on E10 .

Best of luck , :)
God bless
I've been complaining about a strange idle in my GM 6.0 for the past 3 years I've owned it. Not always there, but some days I feel it sitting at a light. Best way to describe it is an electrical pulse. I've changed a ton of stuff. Its not vacuum. Not knock sensors. Not the TB. Not the plugs, coils. Not the catalyst. Transmission mount really helped a lot. Motor mount on drivers side should be replaced, feel it a little in the wheel. Can't see the engine shaking. But if you put your hand on the engine you feel it. A vibration that doesn't feel like a traditional ruff idle. Does not feel or act like a skip. Something electrical. Could be the lean at idle thing cause replacing the knock sensors reduced the frequency. And on cooler days doesn't happen. I've spent enough trying to fix the idle. Now its gonna be the insulation between me and the engine. Rubber mounts. I can't feel it as much with M1 5w30 as I can with other oils. Why who knows
I have also been told they idle lean at a stoplight due to emissions. Mine does the same thing on occasion. It seems to be better with higher octane gas. One owner on Youtube swears by Chevron Supreme. He said no issue what-so-ever with that brand.
I'd use throttle body cleaner and shoot 1/3 of a can in there 15 or 20 min after shutdown. Let soak and run it after. buy two bottles of gumout regane complete fuel system cleaner and dump whole bottle in full tank for two tankfulls back to back. then I'd check the electrical junction and sandpaper the eyelets of all connections and shoot with electronic parts cleaner, replace. Also the grounds. and battery connectors. Shoot MAF cleaner or electronic parts cleaner on the MAF wires and the ambient air sensor in the intake.

Replacing plugs and O2s if old. fuel filter, PCV. also scan PCM for trouble codes but maybe none. these helped smooth out my idle
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