Audi a4, 2,0 petrol. Engine is almost OK in cold

cold weather kills batteries this time of year...heres why..most batteries are a chemical factory..the acid and water separate as the battery discharges..also the chemical process is lessened when the air temps go below freezing by around 50% or more depending on the age of the battery..in extreme cold areas, external heat sources are required to keep engines warm enough to run..in alaska for example,the batteries are taken out entirely and put inside to keep warm..sometimes a fire pit is used to warm the engine from below (red hot coals no flame)..also in very cold weather, the engine oil will get very thick..in some cases the oil will actually glue the engine semi solid..locking it up..if its a cheaper oil that whathappens..I like 20 miles north of st louis in illinois and when it gets below 30 degrees outside i place a under cabinet 350 watt heater(used for keeping food warm to serve) upside down under my engine overnite..this keeps the block warm and the oil thinned out..and works very well for me..my car will start whe no one elses will in my neighborhood..hope tyhis helps you..

Vehicle batteries tend to die during cold weather months since more amperage(power) is required to turn over the engine.


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Maybe vacuum leak it loses when first starting

In cold weather, use 5w-30, in warm weather, use 10w-30.

I’m happy to help further over the phone at https://www.6ya.com/expert/jeremy_69f3cc28d95bf514

A VERY COMMON CAUSE OF THAT IS THE ENGINE COOLANT TEMPERATURE SENSOR, YOU WILL NEED TO VERIFY PROPER OPERATION WITH A LIVE DATA SCANNER, BEFORE U TURN IT ON IN MORNINGS OR COLD, COLD ENGINE LOOK FOR CTS READING IT MAY READ -40 DEGREES, IF SO THEN SENSOR IS MALFUNCTIONING, BUT WILL NOT SET A "SERVICE ENGINE SOON" LAMP WARNING. OTHER WAY TO CHECK IS TO DISCONNECT SENSOR, I AM ASSUMING THAT WEATHER IS ABOVE 20 DEGREES. LET ME KNOW IF THIS HELPS, CAN ASSIST YOU FURTHER WITH UPDATES

without my greasy hands under the bonnet its hard to say but dont be scared of it just because it say ferrari on the front its still made by fiat and uses a lot of common parts ,now what i would do here is to test the mass air flow sensor with my automotive tester to see what happening and if the voltage is varying as it reved up before i start to even think about changing anything ,if this sensor is faulty then its not measuring the right air flow which will not allow petrol to be injected through the injectors hence its not picking up and i think it may be the cold weather thats affecting the sensor in some way ,remember warming up the engine will not make the sensor warm as it still has cold air being drawn in through the inlet pipe

I am guessing you have not changed your thermostat from a summer one to a winter one. If this is the case you need to put a 195 degree thermostat in to replace the 165 degree summer one. Let me know. Thanks.

READ THIS (happy ending so far...):
audi a4 2L turbo quattro, manual transmission with 98,000 KM. Perfect conditions, no oil leaks whatsoever.

Left the car off for two weeks in very cold weather (-10C down to -25C). When I restarted, it started immediately but with heavy rattling noise due to camshaft adjuster not getting enough oil pressure. After 3 minutes of warming up (outside temp.: -12C) at very low rpm (below 2,000rpm), I start moving the car. Still hearing heavy rattle noise. As soon as I pass 2,000 rpm, I get a scary red warning, low oil pressure. Turn off the engine immediately. In 1 minute, I re-start the car and the engine lights check ok, so I drive in first gear super slow (1,200rpm) hearing the same rattling noise. After another minute, finally the noise all the sudden disappears and the car starts running just fine.

Called Audi dealer and they told me that in extreme weather conditions, I should warm the engine for 10-15 minutes if necessary before start moving.
Take away: luckily, I didn't screw up the engine since I was using it at extremely low rpm (easy to do with clutch and manual transmission) until the oil reached full pressure. I am pretty sure now that the problem was leaving the car off for such a long time in freezing weather. All the oil flows back to the bottom, and when I restarted it, the cold oil with high viscosity took a long time to reach all the parts of the engine, specially the camshaft adjusters that are actuated by using oil pressure. Next day, the car started at -9C perfectly without making any noise (as usual). Basically, the longer you leave your audi in cold weather, the longer you might hear the rattling noise until the oil reach full pressure inside the engine. My car took 6 minutes to fix it after couple of weeks in cold weather. This makes sense to me; in fact, in the past I only heard the rattling noise after leaving the car off for a couple of days in the winter.
So far, this has had an happy ending....

It sounds like the fuel is gelled, is it cold where you are and what are running for fuel? If your in freezing weather you should be running blended fuel, straight No.2 will gel at about 25 degrees (F). Take a hair dryer or heat gun and warm the fuel filter up. Or if you can get in warm garage and get it started thin the diesel with kerosene, about 2 gallons to 20 gallons of diesel. Then drive it for at least five miles so the kerosene gets circulated through the system. I've used gasoline to do this too, but only use about 1 gallon to 20 gallons of diesel.

Your coolant sensor may be stuck in advanced timing mode. Change it & the engine will start easy in cold & warm weather. The sensor is located near the thermostat housing. Remove the electrical connector & unscrew the sensor. Replace but do not over tighten, 5ft. lbs. Top off any antifreese loss. Good luck!