So here's the quick story:
99.5 2.8L 165k miles, recently replaced plug wires, plugs, fuel filter, air filter, cleaned MAF sensor,
I was down to 1/8 tank and it started running like ****. Horribly rough idle around 500rpm and barely any power. I floor it from a stop and it feels like I'm barely accelerating. I remembered that the last time I filled up was in the middle of nowhere so I was thinking maybe contaminated gas? I filled up and the problem was still there.

The reason I think that it's fuel related is that I put a bottle and a half of fuel injector cleaner (cheap, crappy stuff from autozone) and drove a couple blocks and it went away. Car was performing beautifully. After a couple days, however, it came back - very rough idle, no power. I stopped at autozone and get some Techron fuel injector cleaner (heard it was decent stuff) and after a couple blocks the problem went away again!

Now it's back and I bought some BG 44K ( Audi dealer said it was the best fuel injector cleaner you can get) for $30 a can and put it in with 3/4 tank full. I've ran half a tank down with this stuff in it and it's still running horribly!!

Could I just need the fuel injectors professionally cleaned? Perhaps it's the ignition cols?

Autozone said I had codes P0300, P0302, P0304.

 

Well you have replaced everything except for the coil pack. I too was suffering from loss of power and had multiple misfires. Swapped out the coil pack with a new one and now I have no issues. FCP Groton has coil packs for a decent price. Give it a shot.

 

Sorry but I can't help but chuckle at wasting all that money on fuel additives.

P0300 is random multiple misfires. P0302 means a misfire on cylinder 2, P0304 is a misfire on cylinder 4.

I'm no expert on diagnosing the 2.8L since I have a 1.8T, but either your coil packs are shot or the ICM needs to be replaced (assuming the V6 has an ICM.)

If you can swap the coil packs (possible to do on a V6?), try that and see if the misfires follow it. If the misfire is still random (clear your codes before doing this) then the ICM should be replaced.

Has your check engine light been flashing?

Good luck, and take my advice with a grain of salt as I have no experience with the V6.

 

Just stumbled across this, I too have the 1.8, but swap the coil packs around. If you are determined to keep adding stuff to your gas, add seafoam. Just did a treatment on mine and it feels like it made a difference. Could be my imagination of course, but on a more serious note, vacuum leak? Sounds like the MAF is getting unrecorded flow. Double check your intake lines and major vac lines and see what you can find.

 

I had a similar issue back when I first got my 01 A4 1.8T. I used Seafoam additive because I wanted to clean the **** out of my engine. I had a serious misfire issue that wouldnt go away after replacing all spark plugs, MAF sensor (which was probably a mistake in retrospect) and other things.

Replaced the coils and bam, all good. Ran like new and there was never another misfire until another coil went bad (which happens more often than I'd like). But its a pretty cheap and easy fix as long as you know which cylinders to replace.

Hope this helps

 

I have a '96 2.8 (12 valve version) so I know some about the 2.8 V6. The coil packs are all on one unit and must be replaced as one whole unit. I recently posted a DIY for 2.8 coil packs (specifically for the 12V). If you have the 30V it should be easier. Anyway, change the coil pack and you should be good to go.

 

Agreed. Sounds like a cracked coil pack. Pull it off the side of the block. If you see cracks, it needs to be replaced.

BG 44K is the best, but it won't help a cracked coil pack! If you've used a whole bunch of fuel cleaners, it's obviously not the issue. When the coil packs warm up with engine heat, resistance builds and the misfgires begin. The fuel additive result is likely a coincidence.

 

The coil packs on the 6 cyl are weird compared to the 1.8t. You have to buy the whole module instead of each one individually which sucks.

 

Just to be clear....that is a 2.8 30V V6 coil pack, the 2.8 12V V6 coil packs are different.

 

i remember i was at orileys auto part store and the store associate was trying to sell me somthing similar and the back of my mind was telling me not to buy that crap