civic0427

In the past 2 months intermittently I'm having an issue with my car where after its warmed up my car wants to start jerking around 4000 rpms and only in first gear. It is an automatic (first problem lol). When it shifts to second gear it is fine at all rpms. My vtec is set to kick at 4k. (Vafc II) It only does its when its warmed up. On my way into work in the morning when I punch it, it seems fine. I also have a low idle issue when I come to a stop. Pretty much narrowed that down to the IAC. Could that be causing the issue Im having only in first gear and starting at around 4k rpms? It is a 01 Civic LX with a 05 EX motor and 01 LX Automatic transmission.

The car has new VAFC II, timing belt, water pump, tensioners, O2 sensor, trans has been rebuilt, and a bunch of other miscellaneous things not worth listing
It seemed to start doing this about 2 weeks after I replaced my secondary O2.

Anyone have any ideas to throw out there?