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Hello all. New to the forum here. I have been relentlessly chasing the idle issue I've been having. To give you a quick rundown, this is what I've done.

Replaced IACV, as well as the gasket & both hoses running to it.
Replaced Map sensor as well as the seal with it.
Replaced the TB gasket
Bled cooling system.
Also spark wise have replaced cap, rotor, coil and iridium TT plugs. (Plug wires looked fine.)
Have sprayed all around for vac leaks to no avail.
replaced PCV valve

​​​​​Upon startup, It will idle to the moon, and a few seconds later drop back down to (I'd guess, no tach) 1500 and surge up to 3000 or so, and go back and forth. When accelerating even ever so slightly, It will immediately buck like somebody who doesn't know how to drive a stick. It will not do so if I am laying into the throttle. When I got the the point of extensive troubleshooting thereafter, I noticed that unplugging the IACV at operating temp created a very sporadic fast idle surge, but this time with maybe a 200 rpm fluctuation, (think the loping sound of a cammed V8). Unplugging the map will make it idle around 2k or so but very rich smelling and sounding. I have adjusted the idle screw to all the way down, and back out 1/4 turn. I have ensured 1/2 inch slack in throttle cable and made sure the butterfly closes 100% I failed emissions due to evap and catalyst issues, and am starting to question Catalytic converter, O2 sensors, perhaps checking fuel pressure regulator and or fuel pump. I'm running out of steam. Any ideas?? PS, if it makes a


​​​ diff, am running A CAI, 4-2-1 headers mated to a Catback.

 
Rep Power: 211

Since you have a cat back bolt-on cat convertor exhaust you could by a cheap test pipe on eBay to temporarily install to see if the CC is the issue.

A new either ngk/ntk/denso (all same company and oem) should be around $35 and worth replacing if you do not know the age of the current one. You can even unplug the current o2 sensor to see if that solves the issue.

Remove and clean the throttle body with a toothbrush and brake cleaner. After reinstalling the TB spray butterfly spring and shaft with wd-40 and lightly greasing the edge (circumference) of the butterfly flap with a synthetic grease such a Napa Syl-Glide. Try removing (from perch's) and repositioning the throttle cable section from firewall to the first cable adjustment mount/perch.

Do a smoke test on it to rule out vacuum leaks. Have access to another ECU you can try?