Like the title says, it's a 2000 A6 2.7t with 6sp manual, about 112k on the clock. When it's cold here (about 40F and below) the car almost doesn't run until it's warm. Press the gas, and nothing changes. The engine won't rev up, it just wants to die. I'm getting a very strong unburned fuel smell from the exhaust as well. When it warms up, it gets alot better, but still very under-powered, and misfires under load.

I did get a p1130 and p0300 code, but it really doesn't tell me much. Long term fuel trim lean on bank 1, and a random cylinder misfire. No kidding, I know it's a bad random misfire. The spark plugs look new, and the coil boots look good.

The only other thing I noticed was that while driving on the highway was that I noticed the coolant temperature dropping slowly down to "c", as if the engine had been off for a while. Then suddenly it would start climbing back to the middle, where it normally sits.

At this point, I'm leaning to guess that there's something wrong with the ECT sensor or wiring.

Anyone have any other ideas, or past experiences?

 

Something is definitely wrong. I just turned 127k miles and mine runs great down to -2o F this winter. Try some gas line antifreeze or maybe some fuel injector cleaner as a cheap fix, but it sounds more complicated based on codes being fired.

 

New updates:

I just got done with some testing. I went right to the ECT sensor and tested it. Right now, it says that it's good. About 3400 ohms at 57oF, which is right on par. I used the mitchell's method of testing by checking resistance at pins 3&4. I also checked that there was ~5 volts from the ecu to the sensor, and there was (when unplugged). Plugged in it went down to about 2.7 volts (I think). This was with the engine cold, not even cranked up one time.

I found one weird thing though. The passenger's side diverter valve hose (pressure side) was popped off, and the hose clamp wasn't tight. I popped it back on, and now it would rev when I hit the gas, but only to about 4k, then pretty much hit a brick wall. I also cleaned the MAF, since a few months ago I was having some trouble with it, but it didn't change anything this time. Driving it around is disappointing. No power whatsoever. Almost feels like it has a plugged catalytic converter now... maybe because of that popped off hose. That would suck.

 

Bad coil pack?

 

I would change the ECT since your gauge is playing up. It cost $7 from most stores. Not much help I know, but it would eliminate it. Do you have VAG-COM? If so, check measuring blocks 15 and 16 (IIRC) to see if you have more misfires on one cylinder, possibly indicating a problem. It sounds worse than a misfire though to me - my car missed and still went like a bullet for a few weeks. Do you have a means of checking fuel pressure? Your pump may not be liking the cold weather. Misfiring under load is typical of a coilpack, which might be good news when you consider the cost of that versus a fuel pump!

 

AGreen, it is very common for our engines in the winter. I have a late '01 2.7L. Everyday I start my car 15-20 minutes before I leave for work in the morning (and these past few weeks have been COLD [from 20F to -10F] but warming her up first is crucial for our turbos. NEVER try to rev your turbos when they are cold. You are taking a huge risk of ruining one, if not both of them. Repairs are not cheap, either ($1k-2k per turbo). Just remember to warm her up first, and you should never have a problem.

 

Coil pack? This car has COP ignition, which is why the P0300 code was so weird.

Turns out, there seems to be nothing wrong with the ECT. All it is is a thermistor, so it's either black or white with those things. Either broken or not, and this one seems to be fine.

I know it's bad to rev a cold turbo, but the way it was running, it wouldn't even let me get out of my driveway. Anyways, the problem became so bad that it ran like *** all the time. I left it alone for a while, then today I went back to it for a fresh startover. I figured I'd try diagnosing it like I would if it were a car at my shop. You know, no history, just "it's broke".

First thing that came to my mind was "wow, this thing runs like it's got a bad MAF sensor." Well, I shut it off, unplugged it, cranked it up, and it ran GREAT!!! Shut it off, plugged it back in, cranked it up, ran like ***. This is a no-brainer now. However, it still doesn't explain my temp gauge dropping to zero...

For any of the Audi specific experts out there, can I drive the car with the MAF unplugged? It'll be a couple days until I can get one, and I REALLY need my DD back.

 

Change your coolant sensor. Very common problem. Your coolant sensor tells the motor how much fuel to deliver depending on how cold the motor is. These sensors can work sporatically which would be why you tested it and it seemed ok. With the gauge acting like you say the CTS is the culprit. Cheap, easy fix and I will almost guarantee that it is the problem.

 

It really is the MAF sensor giving me all these problems. I've got a new one coming for it from audicarparts.com. $72 plus core charge wasn't so bad. I still can't explain the coolant temp sensor. I've never ever seen one as an intermittent problem, but I'll go ahead and get one since it's so damn cheap. If it does turn out to be wiring, that's when it's going to be hard to find where the intermittent open/short is.

 

Problem solved! The MAF sensor works great.

For the past few days I've been driving around with the MAF disconnected, and I've had NO problems with the way the car drove whatsoever! No hesitation, no surging, no misfiring, etc. I got better gas mileage (obviously it would suck with a bad MAF) and much much better, smoother power. I was hesitant to drive it with it unplugged, so I tested it cautiously, working my way to full boost.

Still no clue as to what the coolant gauge thing was all about. It's not screwing up anymore. The MAF reference voltage isn't off the same circuit as the ECT sensor, is it?