1995 Audi A6 Backfire

Hi,
Fisrt of all, You need to check two things: the fuel system, and then the igniton system.
So, first You need to look for:
1. Leaking in fuel lines,
2. If the pressure regulator is ok. It need to mantain pressure about 1 hour after the engine is off; if not, You can be experiencing a leak to return line, or a leak to intake manifold, what cause mixture enrichment and some dificult start when the engine is hot; in this case, simple removing the litle vacuum hose will show you if there are this kind of problem -> You can feel the fuel's smell or also see it droping);
3. If the pressure regulator is ok and the pressure keep droping fast, clean the fuel injectors;
Checked the fuel system, let's go to the ignition system:
1. With the engine off, make a inspection of the spark plug`s wires looking for damages or misconnections that can be grounding the spark before the cylinders;
2. With the engine off, check the primary winding coil wires harness and connector (the smallest wires connected to the coil), looking for misconnection or broken ones.

This is a standard check and if it's all ok you will need to do more advanced checks, specially the data the ECU is sending or receiving, starting by the crankshaft position sensor and the engine phase sensor (camshaft)

Let me know about your progress. By.