Rough Idle and Jerky Acceleration
 

I recently replaced the upper and lower intake manifold gaskets in my '01 Impala. At the same time I replaced the valve cover gaskets, serpentine belt and plugs and wires.

When I refilled the coolant and started it up, the car refused to run for several minutes. After forcing the engine to rev for 2 or 3 minutes, the car finally settled down and I was able to keep it running. I bled out the coolant 3 times to make sure i had all the air out of the system. And ran a can of 44k through it as well. However, I'm still getting a high idle (1,200rpm) when I first turn the car on. And then after a few minutes, it continues to idle rough with minor shudders as the rpms dip by 200-300 every 10 seconds or so. I've also gotten a P0440 Evaporative Emission code a couple of times but it goes away in a few minutes. I'm at a loss for what could be causing this.

Any ideas?

Could this be a vacuum issue?

Could also be crappy fuel

Ive filled up at 4 or 5 different places. Places ive always used