I've had my 2007 Base LS2 to three shops, two private on one Stealership, ( who said they were more than able to diagnosis a rough idle only to now say "there's nothing on the scanner" and charge me $500.00. This is the crap that drives me to drink, and GM dealers are the worst, they will say anything to get you into the Stealership and then WAM ! But I've owned 29 GM vehicles, 18 had Chevy V8's and my last was my 2003 LS1 Vette coupe, and it ran very smooth, So what is it with the LS2 engine, is there some reason it idles rough or is there some kind of injector or computer glitch or secrets with these damn engines ?

 

While I don't have an LS2, I do have an LS3. My C5 had a noticably "rough" idle. I was told it was normal. With the LS3 it's noticably rougher than the c5, but I was told that is normal due to displacement and the stock cam. If the car isn't breaking up and feels like it hasn't lost power most of the time that's just the way it is. These are not lexus's.

 

Can't say mine has ever been rough, even running the current cam it stays flat rpm at idle though it does have minor chop. Smooth as butter once underway.

Odd that none of the places taken could identify cause. No auto tech, but assuming could be plug / wire related or several possible causes.

 

My 2003 LS1 coupe was most defiantly a smoother engine. I'm not talking Cadillac or Lexus, but if this is as good as a LS@ gets, then GM SHOULD be in the Electric motor business. Maybe they can screw them up as well !

 

Just took ours for a drive a bit ago, so engine is warm. It's in garage currently. I'll go give it a start and get a quick phone video. It does have a cam so won't be like a stock comparison.

Think you have something going on yet to be identified. Ours is not stock smooth, but even with cam would not call it rough.

 

Warm idle. Oil temp around 190 after drive a short time ago.


Quality will likely get a bit better in an hour or so. Just shot / uploaded.

 

I have an '05 LS2 and I think it has a rough idle at times. I do ALL of my own work (because I want to) and I have not found any reason for the rough idle. It usually goes away, in my case, at about 200+ degrees oil temperature. So my guess, if you have this problem, is to put in a bottle of Trechron fuel additive. Then get the car fully warmed up and run out in the gears a few times.

 

Does your 2007 sound like a rough idle? Or does it sound like a smooth idle but feels rough to SOP? My 2006 LS2 does not idle rough:

 

Yeah i ran two bottles of Tectron and one bottle of Seafoam. The next thing I'll try is a 150 mile trip down the shore, mines all stock, been garaged all it's life and is garaged now, but it still after 13 years is 21.436 miles, so I think it's "broke-in" But also you sit in the C6 a little low the chassis, so I suppose it would be more noticeable ? I don't know, but I don't like it.

 

My 2012 LS3 idles at 500rpm. I’m sure that causes the slightly rough idle. Put in a small cam and turn idle up to 750 and you will get a smoother idle.

 

I have a 2006 LS2 with 26K on the clock, bone stock motor and idles smooth cold or hot. I know you have had it checked out but could be a spark plug, wire, or distributer cap. .

 

I would say my '05 LS2 does not idle rough.
Are you at the "mercy" of shops and can not DIY?

My first guess would be spark plug wires.
Then spark plug wear or intermittent coil (but I'd think that coil would cause an error code)
Then fuel injectors, get some top tier fuel and Techron as mentioned above and as a last resort send the injectors out for cleaning.

Ruling out the engine, perhaps it is a vibration?
Motor mounts, trans mount and harmonic balance inspection would be the step.
Many have also complained of the torque tube, which is an expensive repair.

That's my two cent comment, good luck.

 

No distributor cap on an LS.

 

Why does it idle so low? Stock they're supposed to idle at 650 when warm

 

No, No your are 100% right, I just enticed by the Dealership excessively stating to me they could diagnoses any problem with the engine, and I said I wanted the fuel pressure tested and the ignition checked, But like the idiot I am, all they do is put a scanner on it, not seeing anything they call it a day and turn the car back to the customer without much more because they already have your car, money and you have to pay to get it back, in my case it was $478.35 to the check-up and I had a "Rattle" under the car which they said was a grille coving the starter and they recommended having a small piece of it trimmed off, and that di get rid of the Rattling noise I heard. But I need to find a good shop who will put in the time and have the hardware necessary to look for more than what a scanner is saying. I have gone over the wiring and everything is plugs in and there isn't any corrosion of loose wiring, and I'm really at fault here I knew before hand that dealerships aren't in the business of fixing problem but more over to remove as much cash from you as possible without a gun., So it's my fault. We had a death in the family, so I'm not able at the moment to address it properly.

 

This is a problem with a lot of "mechanics" nowadays. If the computer doesn't tell them there's a problem, there must not be a problem

 

Yep you are correct. I just did a tune up in my Wakesetter and it has the 5.7 Vortec engine. So guess I had that on the brain when I responded.

 

Or maybe the dealership was right and you are looking for a problem that doesn't exist.

 

These things can help:
make sure plugs/wires are in good shape.
Clean throttle body (gunk gets built up around the blade in the idle position)
Run the gas down to 1/4, dump in a bottle of your favorite cleaner (Seafoam techron etc), run down till the light comes on. this helps clean injectors.

Done this many times on many cars as both preventative and curative treatment. Helps a lot. I do this every 25k on every car as preventative.

 

I also have an 07 base with the Ls2. Mine just turned 70g mi, and also has a little occasional stutter at idle. Sounds a lot like the member who posted the vid of his cammed orange rig. (Nice btw) mine has noticibly less chop than his but other than that, sounds pretty close. Is this something that you noticed developing and got progressively worse? Or is this how it’s always sorta been? My car has always ran like this, and I had mechanics through it back and forwards to make sire i wasnt buying someone else’s problem, the only thing I have put into it is a new harmonic balancer, and that was brought on due to the same feeling, a funky shimmy at idle. My hb was definitely a lil wobbly so it needed replacement anyhow, but that didnt change what I was perceiving as the problem. I was told to keep an eye on my torque tube if things seemed to worsen but otherwise drive it like you stole it..havent had any issues since, still idles like that from time to time..
I am curious to see what you discover though, hopefully it really is nothing. Sucks to lose the five hundred dollars for sure...thanks for the post!