It either misses or revs

I have a 2000 Chevy cavalier LS 2.2L automatic. Over the past 4 months there has been one problem i can't figure out. The car misses or chugs ONLY when i let off the gas pedal, other wise it never misses a beat.

It's not always consistent though.

I've replaced these parts so far with no luck: fuel pressure regulator, throttle position sensor, fuel filter, spark plugs and up stream and down stream oxg sensors

Currently there is no check engine light on, although it does come on every now and then. when it is there the code come up as evap system... which tells me nothing.

I have notice something odd lately. The car doesn't always have this problem, it comes and goes with days as the period of time. On the days that this doesn't happen something else does. When decelerating the car will rev up and down whenever i'm around 30mph. when it revs its jumping up and down from 600 to 1200 rmp. but as soon as i touch the gas peddle it goes away, or when i get close to stopping it stops.

I believe the two problems are somehow related, but they never happen in the same day of each other

When the car is parked it seems to idle perfectly normal.

Anyone got any ideas for me?

The car often smells strongly of exhaust when I accelerate hard