So let.me preface this with I have never driven a Vette with the LS3 prior to this one. I drove an 05 with the LS2 from Florida to TX and don't remember it doing this.

So 13 base vert. Just turned 30,600 miles, car drives perfect. Zero pending, history or current codes haven't looked at misfire counts but misfire monitor is ready. At idle, cold, warm or after driving 2 hours at 80+, doesn't matter. The engine has an occasional shudder both in park and gear (A6). Running 93 octane fuel. Acceleration is perfect and doesn't feel like it's struggling or anything but didn't know if it was normal to do this or not. Motor mounts looked ok, not cracked or broken as far as I can see. Service history shows regular 3-4000 mile oil changes since new and just so I knew what was in it I changed the oil yesterday with Valvoline Advanced Full synthetic 5w30 since I work in a garage it was cheap insurance. The oil was changed just before I bought it by the selling dealer but looked a little dirty for the 800 or so miles on it so that prompted me to just change it. All the plug wires are tight at the coil and plug (wow those back plugs are fun to reach). For those who've had one of these engines for some time I'm sure you will know if I'm being paranoid.
sorry for the winded post.

 

Without a lab scope and what you are experiencing doubtful you’ll find the cause…you can try looking at your misfire monitors if your scan tool has that capability…what part of Florida you in ??…if Southwest bring your car by.

 

I'll look at misfire counts when i get a chance, I'm up in the Panhandle between Pensacola and Panama City

 

Well you can start there…looks like your a bit far !!

 

I think I know what you are referring to. My 2011 GS with the LS3 kind of has a hitch sometimes in the idle. This was on the LS3 cam and still does it on the LS9 cam that is in it now. I just assumed it was a characteristic of the factory cams and the uneven firing order.

 

I've had both a '08 and a '09 base ls3's. I think it's normal to get a little shudder/miss once in a while. I've read numerous posts here about so called "poor" idle quality.

 

I am starting to think it's fine, fuel trims are spot on, no codes, all 8 misfire counts are at zero. Appreciate everyone's input.

 

Funny I was thinking the same thing with my LS2, it’s noticeable especially with a catless straight pipe setup. Almost sounds like it has a mild cam at times lol… you can hear it in the video I took below, I’m assuming it’s normal.

LS2 C6 stock chop

 

Today the car seemed to run rough all of a sudden. Fuel trims are way out of whack, i did a fuel trim relearn and will check tomorrow after driving long enough to set the monitors but one bank pegged at -100% that doesn't sound possible. Check engine light works, no fault codes and misfire counts are zero current and history. Is my scan tool reading something wrong? Am I misinterpreting the data?

 

Take a screenshot of your scan tool data.

 

 

Is this an Autel scan tool or one of the phone app scan tools ??…never seen fuel trims with those numbers…is this with the engine running ??

 

I took a screenshot of a short video of the scan tool screen. It's a Launch X431. I have access to that, a Bosch and sometimes an Autel.

 

I thought readings like that were impossible with the car actually running. Adding almost 100% fuel on one bank and taking 100% away on the other, all this all of a sudden. Fuel trims a couple days ago were in the 5% range. No codes in the ECM, misfire counters zero current or history.

 

Well the car would have to be running to look at fuel trims…what do the long terms look like ??

 

I know it has to be running but i meant not running so poor it barely runs. I will have to check at work tomorrow when I get a break. Still getting around 24-25 mpg average with rural highway driving.

 

Check for vacuum leaks. Cracked or broken PCV lines, intake tube, check intake tube clamps, re-torque the intake manifold bolts, intake manifold gaskets, etc. If it is all of a sudden running poorly and the fuel trims are way off, this is typical of a vacuum leak somewhere.

 

The air intake to throttle body connection was loose, don't know how that would cause 1 bank to run rich and 1 lean, would think that would cause a lean on both banks. Anyways, after fixing that and not finding any vacuum leaks I drove about 100 miles in a couple days and my fuel trims are back in the single digits for long term trims. Idle is improved. So I guess it wasn't tightened properly at some point and worked loose. Will update if there are any other changes. Thanks for the help.

 

Good catch.

I upgraded my hose clamps about a year ago to a constant tension clamp. Allows for a small amount of expansion with heating and cooling. And won't work loose from vibration. And they tend to seal better.

I just measured the diameters I needed and then ordered.

https://www.mcmaster.com/products/co...nless-steel-2/

 

An intake leak will normally affect both banks so I couldn’t tell you why only one bank was very positive.