too lean ?

Deceleration will normally pull more fuel in due to the high vacuum of the closed butterflies creating a rich condition that will cause that popping sound.
if you had a carb, yes. I dont think that would apply with EFI. Isnt popping an exhaust leak? Pulling O2 in and igniting whats left in manifolds? Does 2.0 have a "decel cut" feature that allows you to cut fuel on deceleration, like entering negative values in the fuel table? cut it down to 1750 so itll still idle.