2001 Audi TT 225 Quattro Coupe, 1.8t AMU block, almost 160k miles; mostly stock except for a 3" DP + high-flow cat, spaced-out rear O2 sensor, APR 93 Octane tune. My car acts like it's getting momentarily starved of fuel the past few days. I'll accelerate in gear, and it'll stop, then resume acceleration. When I let off the gas, the RPMs drop a lot faster than normal, and they'll drop to ~500, then jump back to 1100 before settling around 850, which is the normal idle speed for my car. I have no codes stored in the ECU, no CEL (obviously), and all other indicators (temp, fuel gauge, mpg) seem to be within normal specs. What should I be looking for? If it's a vacuum leak, it hasn't been consistent enough to give me a long-term fuel trim code, and I've had and fixed several vacuum leaks over my seven years of ownership, so I doubt that's the cause. Would a fuel filter cause these symptoms? How about a dirty MAF? Perhaps a dirty air filter? Help. I'm lost!