Burgie

Just purchased an 08 z51 with LS3 and noted that upon cold start it will idle rough for about 15-20 seconds and then smooth out. Is this normal or not. It has around 12,000 miles on it and I don't know what type of fuel the prior owner used or if he used Techron injector cleaner in it. Then again if its normal,,,,

beaversstonehaven

Rough idle @ start up was normal for my 2006 coupe with the LS2 and it seems to be normal for my 2013 coupe with the LS3 also. Its not bad but it is there.

Burgie

Thanks, I'll dump some Techron in it on the next tank and see if it clears it up.

cuspid

My 13 does it also at startup, maybe fuel pressure is low at first

bjones7131

My 2001 idles a little rough as well, not bad just a little quiver. From reading the threads it seems some vetts idle rough.

Johnathon59

my '13 does the same, tried different fuel grades and did help some, but 15 seconds is no problem anyway. mechanic says first few seconds the computer system is making adjustments for fuel & air mixtures nothing to worry about.

KX

No need to add anything to the fuel. It is normal at start up for just a few seconds till things warm up a bit. DO NOT MESS WITH ANYTHING!

Burgie

Should one not use the Techron Injector Cleaner on these?

Cherokee Nation

Yes!! You should!! You never know when you might get a bad batch of fuel.I only use Exxon,but you never know.I only get 10 gals at a time,unless I'm going on a long drive then i will fill it up.My 08 ran great at start up,but now with a cam & other mods it idles rough as it should..

Huskerman

On my 10 GS the car would run very rough for a few seconds and then smooth out. I was told it might be an injector that is drizzling a bit after shut off and causing the rough start.

I had been using any average 91 octane I could find. I switched to Shell V-Power 91 and have run it for 6 month's now and the problem has gone away...... Don't know why.........but you might want to give that a try......or any top tier fuel.......

mlsins

EVRose

My 05 must be broken if thats normal. It idles as smooth at start up as it does 20 miles later.

zero11

Sounds normal to me,car's just getting warmed up.I would't run any fuel additives, as long as you run a good name brand of fuel you should good to go.Most service managers don't recommend additives.

RocketDawg

My 09 idles rough all the time when it's warmed up, but oddly enough, not when it's cold. I've tried Techron, GM something or the other, and nothing works. The dealer says it's normal, but I think he just doesn't know what to do. I've gotten used to it so it doesn't really bother me any more.

hawkgfr

Yep mine does...more in warmer weather than cold though. (after car sits overnight say)

franman69

Pretty normal while the fuel pump gets running and vacuum builds.

1rusty1

I test drove a bunch of Corvettes when searching. The one thing I noticed was that they all seemed to idle rough. I passed on the first one I looked at because of it but after taking a few for a spin I figured it was just the nature of the beast. The one I own seems more like a lope than a rough idle.

torquetube

I'm surprised by the number of replies by owners with the same problem. My LS2 C6 settles immediately into a normal idle after start-up. It was like that when it was new, and it's still that way after nearly 120K miles.

The idle has that normal SBC shake to it, but it never gets any better or worse.

Dano523

Yes, about every third fill up, if you are not using top tier fuel with it already in it.

The use of Techron in the fuel is not so much for the injectors, but to keep the fuel gauge sending unit pads in the tanks clean so the sending unit does not go south.

Myself, I use lucas fuel treatment every fill up two fill ups to keep the system clean (incjectors included), then use Techron every third fill up instead to allow it to clean the sending unit pads (not sure how the lucas does on the pads, but know that techron does a good job of keeping them clean so they work.

Also, understand how the tank systems work.
The drivers side tank is the first to be filled up since the fuel fill tube goes to it, then fuel sloshes over to the passenger side to fill that tank up secondly from a slosh over tube on the top of the tanks (once the drivers side tank is mostly filled up). The car will transfer fuel from the passenger side tank to the drivers side tank to use first until that passenger side tank is about bone dry (gauge reading half way full), then will start to use the fuel out of the drivers side tank lastly.

So when adding fuel additives, you need to first add the additives before you start to fuel the car up, then make sure to fully fuel the car all the way up so the additive is mixed in the drivers tank first, then sloshed over to the other tank during the final topping of the tanks to fill up the passenger side tank as well. If you are only filling the car up half way, then the passenger side tank will not see any fuel.

level6

I have a 2009 that I bought new that now has 41,000 miles. It has a good idle at initial start up. It sounds the same after pressing the start button as it does 5 minutes later.

I'm not posting to be disagreeable, just another owner who does not experience any initial rough idle. The engine and ancillary components are stock.