Understanding the problem is key to finding a solution.
First thing you need to understand is when you roll to a stop and idle rpms drop suddenly from any high value down to or close to the desired target idle speed, it is NOT the IAC that is performing that idle drop. The EEC uses SPARK timing to control idle speed, not the IAC. The IAC provides a rough target amount of air that the EEC feels based on conditions should be required for normal idle. However, the IAC does NOT actively try to control idle. Yes, when things are wonky the IAC will make compensations via a learned memory routine, but it is not an ACTIVE correction. IAC corrections are very slow and deliberate.
The act of rolling to a stop triggers the EEC's idle control routine (spark control primarily). This is why as soon as you blip the throttle and/or move the car, idle control is temporarily given up and idle jumps up to wherever the preset IAC setting takes it. Normally this is just a 100-300rpm jump above base idle speed. If you are seeing more of an increase than that then you have mechanical issues that need to be addressed, not electronic ones.
Since the EEC attempts to control idle any time the throttle is closed and the vehicle is sitting still, it can be difficult to pinpoint the problem. You will find you are always fighting the EEC. Using a QH you can watch what the EEC is doing and make corrections quickly, but without it you have to resort to more medieval methods.
Here is one suggestion. With the engine running, crack the throttle to bring rpms up to about 2000 and then let them settle down on their own. Notice what rpm the motor settles to, and then notice the "drop" when EEC idle control takes over. If you are seeing it settle to 1200rpm and than suddenly -wham- it drops to 600, then you have a 600rpm differential that needs to be removed. How?
The excess idle speed can be caused only by too much air entering the system. The question is, is the excess air due to a vacuum leak (after the TB) or is it due to excessive air getting past the TB? Before attempting to set the TB you have to determine if you have a vacuum leak. A smoke test is the only sure way to do this. It is worth the $50 to have a shop perform this test for you. You may find all sorts of things you did not know. I'd have to say that 80% of all SC's that come my way for any reason have vacuum leaks of some sort. These cars are terrible for vacuum leaks and don't think that brake clean or ether will help you find them because most of the time they won't. Smoke test.
If you don't have vacuum leaks then it has to be a leak past the TB. If you really think you might have an IAC issue, simply remove the IAC and put some duct tape over the opening. By blocking it entirely you remove that from the equation. If the car still idles high then you know that is not the problem. Most times it is throttle blade settings that cause the biggest problem.
Setting the throttle blade. First of all, TPS settings are mostly irrelevant. Regardless of what you read, as long as the TPS is between .7-1.1v it's fine. The point is that there is no point in attempting to target .95v or anything else as long as it is not completely wonked. So what is important is that you minimize the amount of air bypassing the throttle blade. Start by making sure that the air bypass screw is completely closed! This is for all applications. Close the bypass. Now the next thing you have to do is close down the throttle blade itself until it sticks. Observe the point where the adjusting screw no longer contacts the throttle arm. This is the fully closed position. If you have done this with the engine running, it will stall. An engine cannot run without air. If you get to this point and the engine is still running, then you have a leak which you must find. But assuming the engine died, then that is a good thing because you can't leave the throttle blade completely closed. If the blade completely closes it sill stick in the bore and cause horrible drivability. So you must open the blade slightly, but only enough so that it doesn't stick. When you feel you have found this minimum position, drive the car and verify that the throttle isn't sticking. If it is, then open it slightly (very slightly) until it no longer sticks while driving around. This is the minimum possible throttle position. PP TB's are bad for having a thin blade that doesn't fit the bores very well. This means that in order to prevent sticking you have to open the throttle further than you would with a stock or better quality TB. This is why people have problems with high idle on these. I can make them work with tuning, but it's rather hard to quess long distance. It's much better to do hands on with a QH so I can watch what is really happening in the EEC.
If you are finding some success after closing the bypass and reducing the throttle blade setting, observer the rpm drop after a 2000rpm goose. If idle settles down to 800 or so and then drops to 600, consider that good. If you take out too much air then it will start to dip and recover. You don't want that. Take it down as much as you can without either having the throttle stick and/or dip. If it dips you'll end up stalling on the road.
Lastly, as you are doing this be aware that there are learned long term trims for the IAC. If you have learned completely wonky stuff over time, then all these adjustments might result in some further adjustments being necessary after some more re-learning. If you get it close, then drive it a few days and see how it "settles in". You might find you want to re-adjust something a little. Without a QH you will never know exactly how much learned correction is going on so you'll maybe just have to accept "good" as opposed to "perfect".
Hopefully this has given you some insight into how the IAC works and why idle does what it does. IAC problems are actually quite rare, and usually the only way they give trouble is if they get really badly gummed up and stick, or if they get a crack or tear in the bellows inside. In either case idle generally will be very high all the time. Keep in mind though that the EEC will still try to control idle meaning you'll still see the "drop" in idle when you come to a stop, just that it won't drop anywhere near high enough. Also, any goosing sounds when shutting the engine off is a dead giveaway of an IAC problem.
