Due to the drop in ambient temperature and changes in humidity that cold weather can bring, your Audi TT may experience problems trying to start up in cold weather. Troubleshooting the cause of these problems can become time consuming unless you know the common problems that most engines experience in cold weather. While a jump start can frequently solve most cold weather starting problems, there are parts other than the battery that can cause problems.
Jump start your Audi TT by opening the engine compartment and connecting the battery to the battery of another car that is running. The red jump lead will connect to the positive terminals on each battery, which will be indicated by a "+" sign, while the other jump cable, most commonly black, will be connected to the negative terminals on each battery. Turn your TT's ignition to the accessories position while it is connected to the running vehicle and allow the battery to gain a charge for a few minutes before attempting to start your TT.
Check the ignition coils of your Audi TT by opening the bonnet and removing the plastic engine cover. There is one ignition coil for each cylinder of your engine and they all sit in a row, above each engine cylinder. Turn on your TT's engine and pull each ignition coil one by one before reinserting it over the spark plug again. If there is no clicking, or spark, coming from the bottom of the ignition coil, then it will need to be replaced. Your engine has enough trouble starting in extreme cold and a faulty ignition coil can only exacerbate the problem. By replacing the ignition coil, you can resolve some cold start issues.
Inspect the spark plugs underneath each of the ignition coils. If there is a black and grey, soot-like substance that coats the spark plug, the spark plugs could be causing your issues. Replacing faulty spark plugs can help resolve cylinder misfires often encountered during cold starts of your Audi TT's engine.
Bring your Audi TT to a licensed repair shop or dealership and have them test the fluidity of the fuel injectors. The fuel injectors are responsible for delivering the appropriate amount of fuel to be combusted by each engine cylinder. Over time, the injectors can become dirty and clogged, which can impact their ability to evenly distribute fuel to all of your TT's cylinders. Cleaning or replacing dirty or clogged injectors can resolve cold start issues that may be caused by an inadequate amount of fuel being delivered to engine.