Intentionally create a vacuum leak and see what happens, it's all about mixture and airflow. I am pretty sure the dashpot is there to keep the throttle plate from snapping closed, it slows it down to ease it back to idle.

 

When i pull a vacuum line the idle goes down, if I put my finger over it to plug it it idles high again. I don't understand why. I am really starting to think that the valve in the throttle body is stuck open, I'm going to plug off the inlet to it and see if it idles down after it warms up.

 

If you verified that your brake booster is causing a vacuum leak why not replace it? if you put all of the adjustments back to proper settings and give the ECM time to relearn how your engine runs you may not have any more issues. One thing at a time us usually the best way to fix anything and with the booster fixed you will be able to test drive it with good braking and no vacuum leak.

 

You never did mention if the surging went away when you disconnected the booster

 

I didn’t clarify very well. I don’t think the brake booster is the problem. In fact I think I have it figured out. Last night I let the truck get up to temp and turned it off, pulled the intake off the throttle body and cleaned with throttle body spray in the inside. Then took a piece of tape and put it over the hole where the air goes for the IACV. Put it all back together. Tried to start it and it would not start. Unscrewed the idle screw about half way and it fired up and idled perfect like it should, I need to find a tach so I can set it proper but I just put it where it sounded right. I drove it for a little bit to confirm and kept pulling over cause I was nervous about the tape. It’s running good and no more surging when I hit the brakes. It hasn’t ran this good since I got it last summer!