harsh downshifts and high idle until completely stopped?

[Darian Key]

IMay or may not have seen previous posts but I fixed my cold start idle issues but still continuing on with this problem. I've replaced now the upper intake gasket and fixed ALL vacuum leaks. After I did this the problem was solved for a while then after driving it about 20+ miles it went back to how it would normally do. As I'm slowing down I can feel/watch the downshifts and then when I'm coming to a stop it sits at 1200 until I completely stop then it decides to. Go down too 800rpm. When I switch from park to reverse or drive the rpms jump and then settle back down. I have a cold air intake so you can hear when the IAC is open or closed and when it's idling high the IAC is opened up because it sounds like a huffing sound. Its a brand new IAC valve and when I unplug it all the issues go away once its warmed up. What might it be? I reset the computer and that fixes it for a little while then back too normal. 97 Xlt 4.0ohv with 163,000 miles. The only code I have is for a fault in bank 1 sensor 2 (forgot which code)

 

[Darian Key]

Bump! Unplugging my IAC does fix all my issues but I just tried to see if I maybe got a faulty IAC from auto zone and still doing the same thing. What could my problem be? Resetting the computer works but only for a little while then back to normal.

 

[JusTheUsual]

Almost sounds like a vacuum leak

 

[rego]

Is there a gasket that goes with them? I don't know.

 

[Darian Key]

Yeah a paper gasket. I had that on there but took it out and put some rtv around the old print gasket and nope still nothing. Like I said it drives perfect with it unplugged once warmed up