[maydk65]

As part of the emissions control there is an evap purge/containment system attached to our tanks. It's purpose is contain vapors from our tanks. When we top off, we can get too much liquid in this system designed for vapors, which does not let the tank "breath" correctly. This breathing problem can cause the engine to stumble. After a time this purge valve can only take so much liquid and will quit working correctly. This is layman's terms. I am sure there is a more technical description for the issue

 

[maydk65]

Here is diagram @Oreo posted in another post on the evap purge valve

 

[maydk65]

There's gotta be something else going on. My car does not have a noticeable rough idle and I am at 46k miles and run Torrie's 93 and E30 tunes. I will say that when I watch the rpm on the SCT, it jumps around 25-50 rpm, but I don't notice it. I theorize that maybe those with a rough idle may have carbon deposits on their intake valves.

 

[maydk65]

My start up idle is 1100 rpm, after about a minute drops to 700. I think Torrie bumped it up on the tunes