'01 A4 1.8T Stock
This afternoon I noticed my car barely had any power, and soon after it started choking or 'hiccuping' while I was in 2nd, 3rd, and 4th gear. At first it was sporatic, but within a few minutes when I came to a stop the battery light came on and the car died. It took a few moments but I was able to get the car started again when giving it some gas, but it barely made it to my destination. After I left the gym it ran fine for the first 20 seconds or so, then started choking again. I noticed it kind of smelled like exhaust when it happened...not sure if that's my imagination, though.

This happened almost exactly a year ago I believe. I took it to a local independant VW/Audi shop and they said they couldn't replicate the problem, or find anything that might lead them to believe there was a problem. I figured it was a fluke and kept driving, then it happened again, except I got a 'check engine' light. I took it to a dealership and they showed a cylinder had misfired, but that was it. They then claimed they could not reproduce the problem. It had been 4 days without my car so I took it back and the problem seemed to have gone away on its own. That made me weary, and I always knew it would come back to bight

I've done some searching on the forums, and the only thing that seems applicable to my situation is I did fill my tank about 10 minutes before the problem started. I noticed to my horror that after I was done filling it I had chosen 85 Octane I find it hard to believe the octane level is whats causing this, though. I read on here that sometimes gas can have traces of water, and that might be the problem. What does everyone think....simple problem of sub-par fuel or is there something larger going on?

 

Fault codes dont lie. If you have a misfire check/change your plugs, and if that doesnt help for 00+ models, its probably a flakey coil pack. Whichever cylinder had the misfire- you should take the coil pack from that cylinder and swap it with a different cylinder, get the ecu scanned again (NOT at the dealer)and see if the misfire follows the coil pack. If it does, youll know the coil pack is shady.

 

Interesting...however this time I have not received any 'check engine' light, so unless the 'battery' light throws an error I don't think there is any yet.

 

Its possible to have a misfire and not a CEL, unlikely, but possible... Its happend to me. If the hiccup you describle is like a hard stutter/buck, its got to be a misfire. If you dont know when/if the plugs have been changed, its probably a good idea to do that. When I had misfires it was due to a hairline crack on2 spark plugs (on the insulator part.) I misdiagnosed it as bad coil packs, so I keep a couple extras in the trunk just in case
If your misfire is bad enough, it will engine speed consistantly which reduces how fast the alternator pulley turns which decreases voltage which could cause your battery light to come on right before the engine finally dies.

 

It does definitely feel like the engine is misfiring, and it's constant....about every five seconds or so. What gets me is the complete lack of power, though. Would that symptom fit into the realm of sparkplugs or coil packs?

 

If a cylinder isnt firing, your going to lose power. Especially if its a constant miss. A misfire can be caused by badspark plugs or badcoil packs, or other unlikely things such as a bad ecu/wires/head gasket.

 

The shop I towed it to today says it's the front o2 sensor, but since the front and back have the same life expectancy they recommended replacing both. I'm also getting the timing belt changed, as apparently if that fails the damage can be catastrophic. Somehow I knew I'd be spending around $1200 to fix all of this At least I didn't wait until a cylinder exploded or something. I'll keep everyone updated on if this actually fixes the problem.

 

In case anyone cares, it did turn out to be the 02 sensor. They also found something interesting...it turns out there's some sort of valve thats normally hooked up to the turbo that recycles unused air or something, and that wasn't even hooked up on my car. Since that has been hooked up It feels a bit peppier...free upgrade!