Let me start off by saying: Watch the video here:
You can see in the video the idle whenever it's dropping will hover at 1200-ish, maybe rise a hundred or two then drop slowly down to 750 (or whatever it's supposed to be at). In the video I gave it some juice to bring the engine speed up, it didn't automatically do that. So keep in mind there is no flutter other than what it does just before it drops down to 750.


Second:
01 Civic EX manual
281K miles

What's been replaced:
Intake gaskets,
EGR
EGR passages have been cleaned (they were completely blocked)
PCV is cleaned and is free of debris
IACV was bought new (it's a DENSO mfg in Japan- OEM was DENSO Mfg Mexico)
Much more has been replaced as well, down to injector o-rings.
I've had the throttle body off, had it cleaned (wasn't much to clean), car has been seafoamed- yeah you should have seen that. You couldn't see through it because it was so dense.

Vacuum leaks:
None- I can put my hand over the intake (tb) when it's running and it will leave a red ring on my hand it sucked so hard. No hesitations like it wants to run, it straight up dies.

Exhaust:
Stock exhaust-
Cat has been gutted (I reset the FI which is why the light isn't on), CAT was about 50% plugged- imagine that with so many miles.
Not ready for a $450 cat piece to be bought.

I've replaced O2's, did a timing belt/tensioners etc.. Since I've had this car in the last two months I've dumped nearly $2,000 into it in parts. I do my own work on all my vehicles so my abilities are up there.

The throttle cables have not been #*&@'d with, the TPS hasn't been messed with and the idle set screw hasn't been adjusted.

With that said I'm stuck. This idle issue has me pissed off. I'm familiar with the IACV's and FITV's in the pre-96/97 vehicles but that doesn't apply here. The issue is electronic somewhere, somehow..... something!!



Suggestions? I'm at the end of my rope here..



Alternately I have a secondary issue with the car. About 10 seconds after starting it will run hella rough to the point of almost stalling out then picks up and runs fine. Does it every time after starting. If I let it idle for 15-20 seconds before driving I can allow it to get past the bad running issue and operates normal. (Aside from the slow idle drop). I'm guessing this is an issue with the cam sensor acting sporadic.

 

Off the top of my head:

-air bubble or clog in the IACV hose(s)
-bad fuel or fuel supply problem
-spark plugs not properly gapped
-needs a valve lash adjustment (may be with that many miles the head needs rebuilding)


Does pressing or releasing the brake pedal change the idle?

 

Negative. No change in idle. Sometimes it would hang and I would double foot the pedals (brake and slip clutch) to get he motor slowed down.

Once slowed down it would stay at proper idle.

Spark plugs:
New plugs, non gapable

Fuel:
Thinking its a non issue. I've been getting 32-36mpg with no bad throttle responses.

Valve lash...
I'll check it. There is some tick from the top a little louder than normal. Roller rockers aren't too loud to begin with.

Iacv air:
Possibly, though isn't the iacv on these just to warm the TB and keep it from icing over and they don't have a temp sensor in them?

I also plan to unplug the cam sensor and see if the stumble goes away. I didn't have time yesterday. I'm thinking it could be a double symptom. Irradic reading by tdc sensor causing the iacv to act up.... Long shot but worth investigating.

 

Update:

video:

New IACV, 150+ miles and that's the solution.

Maybe Honda sites need more actual techs than kids wanting to swap and show off their wheels.. Dissapointed.
(nothing against you LazLong)