For everyone wondering what this thread is about visit here first!
https://ls1tech.com/forums/pcm-diagnostics-tuning/248028-got-nasty-problem.html

First, thanks to everyone who tried to help with my 4.3 Vortec problems.
Ok, after the restrictor plate broke off, my Jimmy was idling way too fast and running lean on Bank 1 cylinders with a wicked miss. After replacement of just about everything, here was the solution. Whenever the restrictor plate is removed the throttle blade doesn't completely close off the port so you have to adjust the idle set screw so the blade close off the port (not too much or your throttle blade will try to stick closed). Here is what was causing the lean condition in Bank 1, my O2 sensor (Bank 1 Sensor 1) was reading a lower voltage than normal. Apparently, any reading other than normal screws up air/fuel mix, so save yourself some time and headache and just replace 02's whenever they aren't reading a normal voltage. Believe it or not just those two things were causing all the problems.
Oh well next time I'll now how to fix the problem. I did do one other mod that I've been reading about. I removed the MAF screen. Now that my Jimmy is running like it should, I have to say that without the MAF screen and the restrictor plate, my 4.3 will gettyup and go. There is a big difference on takeoff without the restriction caused by those two parts.
Well I hope this will help someone who is suffering the same problems and thanks again guys, Scott.

 

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You should be able to get away with removing the divider in the MAF. Do not attempt to bore it out any. Not that I tried or anything (I did...bad results). I am not sure if your intake box is the same as the 98+, but if it is, you need to remove the snorkel off the front of the box. If you are handy with a dremel you can cut a large square hole from edge to edge on that same side of the box for a ton of airflow, while still keeping hot engine bay air out. I did that on my 98. I sanded the edges, and if you didn't know better you would have thought it was supposed to look like that. Underdrive pulleys work excellent on the 4.3L too. They also respond well to catback exhausts. Beyond that you are on your own, but that should keep you busy.

 

Thanks Guys! I still have a small problem with the IAC valve. Seems as though my computor has lost it's baseline on the IAC System. Does the ECM change the position of the IAC pintle according to the amount of speed and throttle position. I had to disconnect my IAC valve. Here is what is happening with the IAC connected, whenever I first start the Jimmy the idle will increase like it should when cold but after a few seconds it drops to warm idle 850rpms. And if I'm driving and I put the Jimmy in neutral while going down hill, the idle is erratic, idling anywhere between 1500 to 1700 rpms. It will actually pull downhill, causing me to use the brakes more. I kinda like the feel of the throttle without the IAC connected and the pintle seated completely. When I go downhill, it's kinda like having an engine brake. Is there an adapter that I can buy that will allow me to open the IAC manuelly, kinda like the old style pull choke?

 

What you should do, is back off (lefty loosey) the set screw on the TB (if possible) just a hair. And I mean a HAIR (maybe a 1/4 or 1/2 a turn). Then pull the cable for your battery and leave it off for 15 minutes. Reconnect the battery, start the engine, let it warm up to normal temperature. Let it run for 5 minutes, then turn on the AC and leave it on for 3 minutes or so. Do not touch the throttle until all of this is done. Then drive it and tell us the results.