First things first. If you have already gotten the idle to just above 500 RPM, I am betting that by the time you get through the oscillations and the idle levels out that you will be very close to 700 RPM. There is probably about 300 RPM to may be 400 RPM of change from the middle of the lower half of the window to the middle of the upper half, but that is just a guess.

The Return to Idle should be, (in my experience), controllable and tolerable for an automatic if you stay with in the middle of the upper half to the middle of the lower half of the window, but each case is different. You will have to make your own decision as to what you are comfortable with, if it even gets into that area of the window where the Return to Idle is affected. You may get to the point where the Idle is in balance, with a decent idle speed, and with a strong return to idle.

As long as you are comfortable with how the engine returns to Idle after revving it up, you can set the Vertical Throttle Stop any where you want. Indeed the Idle can be raised if you turn it in enough.

My point in the last post was to be sure that you understood that the Vertical Throttle Stop Screw setting, can/will a have an affect on the idle speed and its "STABILITY".

When the Vertical Throttle Stop Screw is actively controlling the idle speed, the Idle will tend to be unstable, not wanting to stay at a steady speed, and or, not wanting to return to idle.

Lets see what you end up with.

Note: If you get the adjustment too far into the upper half and, after you rev the engine, it wants to race and not idle down, don't panic. Rev the engine with the Red Stop lever on the valve cover. If the engine does not want to idle down, just push on the Red Stop lever a little, this will compress the spring plunger in the end of the screw and the engine should idle down. If you push hard enough it should shut off. You can have pressure on the Red Stop Lever, and back off the Vertical Throttle Stop Screw until it will idle down on its own after the engine is revved up. It is good to know where your setting limits are to get the most out of a setting.

Perfect Governor operation depends on perfectly balanced settings. When you change one setting, it throws off the balance and has a side affect. The trick is to know how to make a setting change and keep everything in balance.

So to get this straight... When you say:

You mean to do it first and foremost with the vertical throttle stop, right? Ill do it that way, and notionally when I get the spring in the right range via adjusting it in, Ill get to roughly 700rpm, right?

Then I can readjust throttle linkage, verify return to throttle, etc., etc., tweak as needed, etc., right?

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

Yes, It is easy to get at, and as long as you know about the side affects that this adjustment has, you will be able to identify when you get to the "productive" limit, ( when the return to idle is too slow, or the Idle speed is unstable).

It is a cheep shot. Some one may have turned it by mistake at some point in the cars life. There no real risk here, (unless you try to drive the car when the return to idle is too slow), as, you can get to the point where the engine will not want to return to Idle, ( and I encourage you to find that point, if for nothing less than your understanding of the control you do have), and then just back the adjustment off until the return to idle is how you want it. No big deal here, as long as you know what to expect.

No promises of that. As you turn the Vertical Throttle Stop in or out, you are changing the Throttle Spring Tension that is ultimately pushing against the Fly Weights.

I think of it as a push of war, where if each side has three people, and if each team's combined strength is equal to the others, there is a balance of power, each side is equal too, or cancels out, the other side. If one person on one side looses some of there strength, the other side will be able to move the other side a little bit. If one person on one side gains some strength, their team will be stronger and will move the other team.

In the Governor, one team is the Fly Weights, and the other is the multitude of springs that combined their strengths to push back against the Fly Weights.

Adjusting the Vertical Throttle Stop Screw changes the strength, increasing it or decreasing it, of one side in the Governor push of war.

What your idle speed will be when you reach the point where the engine will not idle down as you would like, is going to be determined by the setting of the Idle Governor it’s self.

From the information you have provided, (that is why I wanted to be sure I understood exactly what your engine was doing), I am fairly confident that at some point, someone for some reason, backed the Vertical Throttle Stop out, which lowered the idle speed and put the Governor in a state of imbalance at idle. I am hoping that when you turn in the Vertical Throttle Stop In, that your idle will be in range of where you want it, and that you Governor will agine be in, or closer to, a balanced state at idle.

My engine searches at idle when it is cold, and when I lightly step on the throttle when it is warm it gets worse. It can be a bugger to creep along in first or second, (it is a manual). On top of that, it returns to Idle way too fast for a manual, and I have to leave a slight pressure on the petal when shifting to be able to shift smoothly.

My idle was at 800 ish, and I have turned in my Vertical Throttle Stop a little and the Idle is now at 1100 ish. In my case, I need to go into the Governor and lower the Idle speed. Since your idle speed is low, either someone lowered it, something internally changed, or it was that way out of the box and no one addressed it. I am betting on the, "someone turned the Vertical screw".

Go ahead and play with it, paying attention to how the engine sounds and responds to throttle input. You can always put it back where it is now.

Yes, If your idle speed gets to where you want it, and the return to idle is good, (the car slows down when you take your foot off the pedal), then you are there. Tidy everything up and call it a day.