misfiring and bogging down - Stumped with my 99 A6 2.8
 

My beloved A6, Stella, has developed a problem that has me stumped. I returned home from deployment, and she had sat for a year. So i changed the oil, added some Sta-Bil, and drove her nicely. I drove her maybe two months, when suddenly, she bogged down heavily on an uphill. I barely made it home, and too much throttle would kill her, so I had to limp home at an embarrassing 15 mph. I've been stumped ever since. I've had her 9 years and driven her almost problem free to 166k miles, so I've become quite attached to her, and would much prefer to fix her. I crewed on Helicopters, so i'm semi-mechanically inclined, just never spent enough time with cars to be an expert.

If anyone could help with any sort of issue, I'd be ridiculously appreciative.

So here is what I know.

She starts, and it sounds terrible. I can rev her up to about 3400+ and she whirrs right along, sounding reasonably good, but too little throttle and the revs jump from 800 to 1800 then back, ramping up and down on its own. At first I thought the fuel pump may have started wearing out, but she came back with about 75-80 pounds of pressure after I tested it, which seemed a bit high. I replaced the spark plugs, which helped enough that she will now idle without having to give it a little gas. I popped the coil packs off and I can see a spark in all of them.

Also - the battery won't hold a charge, without doing anything, just leaving it connected, for more than 3 days. The OBD diagnostic port wont return any codes, which has made troubleshooting much more difficult. it comes back with "READ ERROR" at Autozone.

I just got out of the Army, and now i'm in college with a new wife and a kid on the way, so money is rather tight. That's why i'm trying so hard to only have to buy one part to fix it. I've heard the ignition coils can go bad in these, but don't know if it would still spark in all coil packs if this had happened. The Fuel pressure seemed high, and a friend recommended fuel pressure regulator, but as I said, I'm trying to be very sure before I purchase any non-returnable parts.

Any info, suggestions, advice, no matter how small, would help greatly.

Please, help me save Stella!

Give the air flow sensor a good clean, and clean off the plugs as well. This will eliminate a few things and it quite easy to do.

Ignition coil failure is consistant usually rather than flat spots at certain RPM so I'd be surprised if it was a bad coil.