The bitch about idle is, it seems like every car is different. For example, my '01 H/C M6 SS idles fairly well with the stock tables and only needed a few adjustments. On the other hand, my friend's cam-only '00 A4 WS6 needed a little more tweaking.
Usually, spark is a major contributor to idle issues. So, keep that in mind while working on idle. Bi-directional controls will be a lifesaver for spark. What I usually do first (after some initial spark adjustments) is set the desired airflow table using the RAFIG and RAFPN (for autos) by logging from several cold starts. One trend I notice here is the curve tends to smooth out a bit (kinda looks more like a hockey stick). Once that is done, you have your base. Throttle cracker will be added to this base and the throttle follower will be either added or subtracted from this depending on changes in RPM. **On a side note, I usually adjust B4308 based on the changes I made to the desired airflow. Just be aware of the different coolant temp scales between the 2 tables.**
The next thing I do is take about 50% out of the cracker & follower airflow tables (B4309 & B4315). My theory in doing this is, there's more of a cam now so less compensation is needed. The same theory can be applied to the 3 airflow tables (B4512, B4514, & B4515) that control the IAC. Their overcompensation can be the cause of some surging too (mainly on A4's). Tweaking the throttle cracker further is best done by logging the idle pid for it. Then you can see when it's being applied and whether or not it's jumping between cells (up...down...up...down) causing surging.
IAC effective area should be left alone assuming airflow to the IAC valve is still unobstructed. Epoxied TB's can be the cause for some problems with idle airflow. In that case, you can try tweaking this table. But, chances are it's just easier to get rid of the epoxy.
The tricky part is doing all of this while keeping an eye on spark. Jumping between the high/low tables and the base tables can be the source of surging as well. Usually, cam'd cars like 42~45 degrees of timing during decel under 2400 RPM. The trick is to figure out where your grams/cyl are at for 0% throttle decel and set the cells around there to a single number (ie all cells .08~.24 and 1200~2400RPM to 43 degrees). Generally, you want to do this until just before idle (or when the TCC is going to unlock) in the high/low and BSIG tables.
Playing with those tables is the best way I've found to tackle the real issue...surging. To answer your original question though...the TC is always added to the desired airflow (when enabled) for the given MPH/RPM cell. Too little can choke the motor down and too much can cause a cruise control effect. The TF is subtracted from the base (desired airflow) during increasing changes in RPM and added during decreasing changes in RPM. This essentially softens the blow of changes made by your right foot for both more or less throttle.
Well...that's my $0.02 on the matter. Hopefully it helps someone.
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