2000 Audi A6 Popping noise with MEDIUM ACCELERATION in driv

I changed the spark plugs and changed the oil, the engine sounds fine when its in Park or Neutral and I Rev the engine. The engine makes a Popping noise and doesnt accelerate correctly if its at 1.5 RPMs and I accelerate NORMALLY when in DRIVE and the car actually moves, cause I put parking brake on and accelerate while in drive and no popping noise. I need to LIGHTLY accelerate or take my foot off and floor it so that it accelerates and doesnt make that POP noise. Every time I try to accelerate NORMALLY it makes that noise and loses horsepower, so I take foot off and floor it. Also, I noticed OIL in 1 of the spark plugs when I changed them.