No check engine lights, problem started a while ago, starts running very rough like it dropped a couple cylinders or when I just let off the throttle real quick it falls on its face like it's Jake braking off a dead cylinder or 2 then picks back up, shop told me coil packs and I replaced both with duralast, ran worse out originals back in, problem resurfaced later but worse, I've tried plugs, wires, both packs again, I've tried running fuel system cleaner, shop told me there was no injector problems, good fuel pressure at the rail, I'm mostly looking at ignition related problems, all motor sensors were replaced a few years ago, could it possibly be the 02 sensors or something with the cats? They're new too, still runs with enough power to move well but very rough.

 

Unplug the front O2 sensors, (which I suspect is all ya got....) and see if it runs any better.

 

I tried unplugging the 02s, it ran the same which was still pretty off even after a couple minutes. When the issue presents itself there's also a lot of noise from seemingly the cats almost like a muffled combustion, but when it's running normally everything is perfect. A lot it like the down on power, seemingly dropping a cylinder or two, running rough point to icm, just hoping it's not entirely that because they're hard to find

 

Try physically removing the O2 sensors from the exhaust. Might be your cats are broken down, and when the pieces bounce around right/get hot, the cause a restriction.

What plugs do you have in it?

 

Cats are new, originally had them out and put them back in because I thought low back pressure could be the issue, the exhaust is stock up until where the two banks come together under the truck, I have an x pipe which I've been told couldn't be an issue though it seems that's where the weird sound could be coming from, after x pipe straight to cats then just the rest of the system, no mufflers. It has newer ngk plugs, napa wires. 6 pack coil is prenco, 4 pack is Delphi

 

Try a cylinder balance test. Get the engine warmed up, and idling reasonably. Disconnect the IAC motor. (will quite likely set a code) Then, pull one spark plug wire at a time, and see what idle does. Keep track of which cylinders do what. Then see what the bad ones have in common. On cylinders that are working properly, there should be a noticeable change in idle, if there isn't much, or any... change, thats one of the bad cylinders.

 

A couple questions, what and where is the IAC motor, and by bad cylinders would that be following back to what exactly controls the spark for those individual cylinders?

 

IAC is on the throttle body, four pin, square connector. (I think its square anyway....)

Yeah, I am curious if you have a bad coil. one coil fires two cylinders..... so, if you have to bad cylinders, and they are on the same coil..... it's bad. If you have more than two bad, see which 'pack' they all go to. (4 cylinders, or 6...) If they are spread across both of 'em, things get more interesting.

 

Both the 4 post pack and 6 post are brand new, even the old ones tested okay for continuity and resistance, that's why I'm curious about potentially the icm being bad because I've read on other threads it causing either 4 and 7 or 5 and 10 I think it was to have no spark, and with all other ignition parts that I know of being new aside from that single module, what other guesses could I go after

 

Just read another thread relating to IAC motor issues, my truck has a leak at the driver's side exhaust manifold, just a small ticking sound coming from it, could that cause any issue? Or could the x pipe in the exhaust cause any issue?