Are all of your injectors identified with the same color paint dot? It doesn't matter what color they are so long as they're all the same.

Is the dizzy rebuilt with OEM parts, or one you bought that was already rebuilt?

Is the intake tube from the air filter to the engine tight and has no leaks, all hoses attached?

Any vacuum hoses missing or misrouted?

If you have EGR, is it working and is it clean?

 

Are all of your injectors identified with the same color paint dot? It doesn't matter what color they are so long as they're all the same.
Yes all ordered and installed at the same time "black" dot

Is the dizzy rebuilt with OEM parts, or one you bought that was already rebuilt?
It had a cardone when I got it and I put a OEM hitachi from a junk yard and put a new bearing in it. honestly have swapped between the Cadone and the rebuilt with absolutely no change

Is the intake tube from the air filter to the engine tight and has no leaks, all hoses attached?
Sorry I knew i forgot something I replaced. Yes it was the first thing I replaced.

Any vacuum hoses missing or misrouted?
Checked and double checked all vacuum lines against the FSM diagram.

If you have EGR, is it working and is it clean?
New EGR valve and I clean the entire run inside the Intake plenum.

 

Have you done a vacuum test? I know you’ve confirmed routing/connection, but if I were in your shoes, I would put a gauge on it and rule out vacuum leaks before proceeding (if you haven’t already).

IACV is not out of the question, but what you’re describing is not the most common failure mode for an IACV in my experience. Does the idle smooth out/come up as the engine reaches operating temperature, or does it sit sub-700 in drive even with a warm motor?

 

Have you done a vacuum test? I know you’ve confirmed routing/connection, but if I were in your shoes, I would put a gauge on it and rule out vacuum leaks before proceeding (if you haven’t already).
Sorry I have done so many things with the X I forget. I do a smoke test each time I do something, no leak in sight. I plug in right where the brake booster connects to the upper intake plenum, and I disconnect the intake airbox and plug it so the smoke does not contaminate the MAF. The vacuum is at 18.


IACV is not out of the question, but what you’re describing is not the most common failure mode for an IACV in my experience. Does the idle smooth out/come up as the engine reaches operating temperature, or does it sit sub-700 in drive even with a warm motor?

I know the typical IACV failure tends to have a pulsating idle or no Idle at all.

1. In park, starts and idles around 12-1300 for about a minute until it warms up a bit, then idles around 850 in park. Idle is pretty smooth but I have had the p0300 trigger sitting at idle.
2. when put in Drive or Reverse Idle drops to anywhere between 720-680ish.
3. drive for a bit and sitting at stop lights in Drive idle is a bit rough and and is around averages around 700 not steady but not really pulsating. if I kick it into neutral it goes to around 775-800 and smooths out again, but drops back to rough once I put it in Drive.
4. at Idle, parked or stopped in drive and I turn on the AC. nothing happens idle stays rough and does not increase, but if I blip the throttle over 1200pms while sitting, the idle will increase to about 850-900ish rpms and is more smooth. but once I drive and come to a stop again it will go back to 720-680ish. that is repeatable.

I've read the FSM and did the Base and Target idle procedure to try to get a steady 750 target RPM, and I've adjusted the idle screw all the way in and almost all the way out and it does change the idle but once it get put in DRIVE I get 720-680ish and rough. It's like the TPS, Cam sensor and IACV get together and decide for themselves.

This is totally stumping me.

 

I was guessing based on everything else that you had pretty conclusively ruled out vacuum leaks. Just making sure (as someone who’s spent weeks chasing ghosts that could’ve been sniffed out by a simple test).

The age-old wisdom is that multiple misfire is pretty much always electrical…

Except when it isn’t, and with these symptoms I’m not convinced of anything. If you reset the code while driving, does it set it again while you’re under load (with the throttle consistently at 1/4 to 1/2, in highway driving)?

If the misfire is confined to idle (or return-to-idle/foot off the gas) conditions, IACV may be your best shot at this point.

 

Misfire is 100% random. Could be while driving, cold warm, never repeatable. After replacing everything I have it does tend to not trigger while actually driving and you could hear and feel the misfire before I replaced everything. Now you can’t hear it but the rough idle and p0300 still happens.

 

Oh and it was most noticeable on deceleration. So before the major replacement i disconnect the exhaust right after the front catalytic to rule out a plugged catalytic and sitting in park if you blip the throttle to say 2-2.5k on its way down you can defiantly hear the misfire. It not so noticeable now

 

Ok, I’m pretty sure this is not a typical fix for p0300…. But after cleaning the IACV-AAC code has gone away and it passed CA emissions with flying colors. Again this prob isn’t the normal fix for this code but it fixed my issue.