Like any other car on the road, the Audi TT features an exhaust manifold that routes the combusted gases from the engine to the exhaust system's piping, and eventually out of the muffler. A number of symptoms shown by your Audi TT can indicate that there are problems with its exhaust manifold.
If there are exhaust leaks from the manifold, your TT will experience a loss in fuel efficiency. Listen for noises such as hissing and popping from the underside of your TT as the engine idles to identify an exhaust leak coming from the manifold. When the air is leaking out prematurely from the exhaust manifold, you may also notice a louder exhaust note as you accelerate your engine.
Over time, the exhaust system in your TT can become clogged with contaminants and particles that are emitted from the engine as combusted air travels out of the manifold. Should the manifold become clogged, you can purchase exhaust cleaning solutions that will help to loosen the contaminants and push them out of your exhaust system. These solutions are often poured into the gas tank and run through the engine's fuel system.
Because the exhaust manifolds are made of metal, they can become corroded over time, especially if you frequently drive in an environment that is exposed to excess amounts of road salt and dirt. Similar to a leaking manifold, a cracked manifold will cause a decrease in engine efficiency and fuel economy because it is leaking exhaust gases prematurely through the cracks. While costly, the only way to correct a cracked manifold is to replace it with a new one.
The exhaust manifold on your TT can also become loose. If you or a mechanic have recently performed exhaust work on your TT, the manifold could have mistakenly been left loose. Check the bolts that connect the exhaust manifold to the engine and ensure that they are tight and snugly connected. If the manifold is loose, your engine will likely have a very rough idle and will not accelerate smoothly.