With you powering the constant and switched power at the same time will make it harder to start. I learned this lesson while testing my harness before actually routing it in the body. If you power both up at the same time, the IAC doesnt reset and go to the park position properly. As for the fluctuations in rpm etc, the pcm is trying to learn. If you warm it up and datalog, you can load the data in the spreadsheet and get the VE table closer. The ideal situation would be for the pcm to not have to make any correction for fuel. Real world is that it does... especially with weather changes but getting the ve table closer to ideal will help. I would set it up with a battery disconnect switch and an ignition switch on the test stand. My engine would surge with a constant throttle position until I got the VE table dialed in closer to what the engine was happy with. A test stand is not good for tuning. You have no real load on the engine, You can tune a few ve cells in the closed throttle table and not much more. You can also play with the idle spark to get the smoothest idle if your cam is other than stock. Actual tuning can only happen with varying the load and rpm.