I had a bad balancer that I changed over the winter. At same time I added a LS6 manifold, Vararam & power duck, and had my TB ported. Everything was running great until about 200 miles and then the idle started sputtering.
I used up the gas and refilled with my usual, 93 Shell, cleared all codes and it still is rough at idle. There were 0 codes. Sometimes at a light it is steady and smooth and then it goes rough and sputters. Under throttle it's responsive has great pep and just wants to go. Any Thoughts? Mark

 

Pull your codes and see if anything is reporting. Also look for air leaks such as the air bridge coming off the bottom of it. PCV line to the intake should be looked at too.

 

As stated, no codes were present. All hoses and duck clamps are on and checked for fit.

 

Could be that duck in your duct! LOL Sorry,I couldnt resist! If you are quite sure your have no vac leaks and you have no codes,you may need a dyno tune.

 

Loose spark plugs/wires. Maybe just need new plugs.

 

Thanks, but I changed them when I was in there.

 

The ported T-Body-LS6 intake and especially the Vararam require some tuning to correct idle issues---Most likely your LTFT's are way positive pointing to a lean condition caused by the mods
You 1st should log your long term fuel trims and get them all at "0" or slightly negative--
THEN--normally you need to ADD a % to the "desired airflow table" both in gear and P/N--I would start with 10%---When your car is 1st started it runs in "open loop" til the collant reaches 140* after warm--it uses a timer in open loop like 20 seconds then it switches to 'closed loop"
the LTFT's and 02's are not used in open loop mode--In closed loop the ECM adjusts the fuel via the fuel trims to get the fuel back to the stoich of 14.68--IF the trims go beyond +/- about 20% for a long time you should get a code---But short trips won't trip the codes--
Most likely the trims have gone beyond 20% and the ECM can't correct enough to get back to 14.68 causing a rough idle or can cause surging or dieing--As you say when mashing the throttle it still works fine---That's because when the throttle goes past 64% it goes into POWER ENRICHMENT mode and the fuels trims are again not used--and fueling is regulated by the PE programmed table--Stock PE tunes are very rich from the factory-So the added leaness from the mods actually makes more power
Stock PE fuel is like 11.5 AFR (pig rich) and adding your mods gets it to maybe 12.4-- i tune DD type cars to run a safe 12.5 --A more of a street racer car maybe 12.7 and a dedicated race car to 12.9--hope this expains it ti you some---

 

Thanks, I do understand some of it. I wonder if I explained my mods and idle situation to ECS and sent them my PCM for their mail order tune, would that get it corrected? I don't have anyone close that I would trust for a dyno tune. Thanks, Mark

 

I could see the vavaram causing it to act up while driving but at idle it really shouldnt. There are quite a few people running that combo without a tune as well. Running rough sounds like a spark plug or a bad wire. I had the same problem and it took quite a while for the 0300 code to come up and then a loose wire fixed it right up.

 

I feel like a complete dumb $ss. I found the problem after another drive this afternoon and cool down.

It was a loose plug wire on the drivers side very back plug, #7, I think. Thanks to mchicia1 and baxsom for the heads up on the problem. Such a simple fix. I sure it will run better on 8 cylinders vs 7.

Thanks everyone. Mark