[s-cars] bad tank of gas?

[Steve Marinello]

A little help requested...

Happened by a Chevron station with somewhat cheaper gas about four weeks ago and filled up the S6.  Drove about ten blocks...and it started missing and bucking intermittently.  OH SH*T!!!  Bad gas??  I was about o get on the interstate anyway, so up I go. Ran like crap for a bit and then cleared up.  Okay, good.  Next day, head to work.  Started out fine, went bad for about 15 minutes of the 45 minute drive and then cleared up again.  Time to head home and it started up missing after sitting in an uncovered lot in 85F heat...black car, just in case anyone thinks that might account for anything.  Ran badly for ten minutes; cleared up again. The next day it was worse, with intermittent good running, so I went down to the local FLAPS and got some Marine/Auto Fuel Treatment that is supposed to be pretty good.  It got better; it got worse.  

I headed out for a two week business trip that involved too many planes (another story) leaving the S6 with a 1/2 tank in the garage.  On my return, it fired up smooth, and went crapping again after a couple of miles. Ran it down to reserve and added another can of treatment with 5 gallons of new fuel.  Same.  Saturday I pulled the plugs.  All showed some evidence of crap having run through, but all electrodes were clean.  The #3 plug was not exactly tight; #1 had a discoloration running up the ceramic, but nothing more.  I replaced it with a good looking old one from the avant.  Started it up and killed one plug at a time; they all made it worse.  Did the same with the injetors; same thing. Same old story this morning, culminating with running it down to near empty on the way with it now being worse than ever.

Was it really bad gas?  Vacuum leak, MAF, ???  Any ideas from any of our experts?  Hard to tell with that kind of info, but it was running fine before the gas fill-up.  I guess it's time to have someone scope it and see what they can find.  

TIA,

Steve