Hayabusafalcon

2006 B7 A4 2.0T quattro 6-speed Tiptronic. 233k miles. Daily driver. Michigan snow belt.

This is something new to me so I thought I'd recount my experience from yesterday. Something interesting happened.

It's been cold-cold here in Michigan. 9 degrees F overnight and a Hi of 16 F in the afternoon.

On the drive into work in the morning, a CEL P0299 appeared, low turbo output. The car seemed to be running normally. I reset it with my OBDII code checker which I carry in the car. It reset okay. The drive in was in heavy snow falling.

Here is where it gets interesting.

The car sat for about 12 hours in the parking lot. It started fine, but on the drive home I immediately noticed a lack of power and the engine would not rev above 2,800 rpm. I initially had problems getting above 48 mph. I limped the car on the back roads for about 10 miles. No CEL.

It seemed like the turbo had quit. The car ran fine but would buck while shifting 2nd to 3rd in automatic mode. I had to manually shift to keep it from bucking.

Gradually over the next 10 miles or so the car began to come out of it. I could hit 65 mph in 6th so I bounced back onto the expressway. Still nowhere near full power but the turbo did seem to be functioning. Got up to 75.

I checked it out when I got home. Everything looked OK externally in the engine bay. Since the car seemed to be choked down, I pulled the airbox lid and checked inside. Found chunks of snow, ice pellets, and water droplets. The filter, an accordion paper filter (Mann, OEM), was damp to the touch. I pulled it and put it in the house then went back out and installed a used (but clean) filter I had on hand.

A test drive revealed the car was back to normal operation. Hmm?

Back at the house the Mann filter had warmed up and sure enough there was drops of water coming out or it. The darned thing had frozen.

I've never had that happen before. In any car.

Yes, the snow screen from the airbox....I removed it years ago. I don't know where it is or I'd put it back in. My thought was it is another useless do-dad so I may have chucked it. Maybe it's not...so useless.

Has this happened to you guys? Comments?



BTW- she ran just fine this morning. (Clear and cold 0 deg. F).

All the best, Haya....

uberwgn

Haya, you should see if you can buy the "cold weather" version of your air filter that has the white gauze covering on the intake side. It's specifically for preventing this issue.

Hayabusafalcon

Super-uber: Thanks. That makes sense. I'll give that a try. Haya....

uberwgn

Probably going to be necessary with your snow screen removed...

Hayabusafalcon

Long over-due follow up. June 30, 2024
After the crazy freeze up event with the stock Mann filter I went back to the washable-reusable type I had been using for years. I've never had a freeze-up with this type. Never....before or after that episode. And I have used the same makes (Auto Dynasty and Spectra brands) in all of our vehicles. I used to use K&N until they got so pricey. These are as good or better than K&N or any OEM filter. I have a red one for the Highlander purchased 2015 still in use today. Yep, so they hold up to repeated washings very nicely. Recommended. Also see my tips on airbox stuff. Scroll down.





Air-box DIY service tips and tricks:

The A4's clam-shell style airbox is a bee-otch isn't it? I hate the thing.

1. If the shell clamping screws strip out, drill out the holes for a larger wood screw or deck screw. Just screw the new one in place. Easy-peasy, no thread-taping required. I found some cabinet-makers screws with wider heads. They work as well or better than the original fasteners.
2. Don't fool around trying to pry the shell halves apart in place. You'll just scrape up your hands trying to wedge the old filter out and the new one in. Rather: Remove the ram-air duct, disconnect the MAF sensor cable, undo the outlet hose, (Vice-grips work nicely on that spring-clamp), and pivot the inboard part of the shell off its hinge point and then lift the shell away. Now it's easy-peasy to do the rest.
3. If the interior airbox foam has broken down and is coming off in pieces, remove all of it and vacuum it out. You may have to scrape some. Those foam-retaining grid sections kind of wedge in place. DO NOT break them out. No! You will need them. See next tip.
4 You can leave as is with no foam, or you can replace the foam inexpensively yourself with a pair of scissors. On mine some of the grid had broken so I used short deck screws with flat washers to hold things together. Alternately good foam-type double-sided tape like that super-sticky 3M picture hanging tape is another option to hold the closed-cell foam in place. I redid my airbox foam five or six years ago and it has held up remarkably well.
Link to typical closed-cell foam that works nicely, 8mm thickness:

EVA Foam Sheets 35x50cm Handmade DIY Craft Cosplay Model 1~10mm Thick White | eBay