2002 Accord 3.0 V6 Erratic / Unstable Idle at Cold Start ONLY

Hello,
2002 Accord Sedan 3.0L V6 w/ ~199K mi


Owned the car for about the past 6 years and it has ALWAYS behaved like this since the beginning (2012). Sometimes it may be a little more or less obvious but every time nonetheless.



Every time you start the car up from a cold start (i.e. sitting overnight) the idle will briefly rise to ~1100 RPM, then within 1-2 sec. quickly drop down to ~750 RPM, at this point the engine starts to stutter and almost feels like it is about to die, then the idle will rise back up to ~1000 RPM and run perfectly smooth before settling down to the usual warm idle speed of ~750 RPM.


Over the years it has not gotten any better or worse, so I have not been inclined to start part swapping unless the engine would actually die during idle, which it still has never done.


I keep up with basic maintenance (oil, trans, air filter, plugs, etc.) and clean the throttle body every so often (which does not help w/ this problem). Recently the car just had a timing belt job, again no change in behavior.


I am considering replacing the idle air control valve (IAC).


Any thoughts on whether that is the next best step?...or how can I troubleshoot before replacing anything?


The valve clearance was adjusted ~80K mi ago...could the valves tightening up cause this type of symptom?


And just to state again, it has been doing this for the past 6 years since ownership and has not gotten any better or worse.


Thanks.

I think you could tell if it is the valves with a vacuum gauge. If there is fluttering, then probably the valves.

**Update**

I replaced the idle air control valve or as Honda calls it the rotary air control. Also replaced both throttle body gaskets and thoroughly cleaned both the throttle body and spacer while apart. All Genuine Honda parts of course.

No difference made.

At cold start or first start of the day (here in TX that is now 90+ degrees) the idle briefly touches ~1800 RPM (I had mis-stated 1100 in the original post) and then quickly drops down to ~750RPM where the idle then stutters for a bit before then going up to ~1100 to 1000 and then eventually settling down at ~750 when the engine warms up.

Vacuum lines are in good shape.
Although I did remove the MAP sensor and noticed the O-ring was pretty flat so I may go ahead and replace the MAP and O-ring in case any un-metered AIR is getting in.

Any other ideas on what causes this brief stutter in idle?

Occurs only at cold start and the car does not have any other performance or idle issues.

Thanks.

Replaced the MAP o-ring and PCV valve (OEM of course) and still no go.

***Update after 1yr***

So turns out this all seems to be caused by carbon build-up or dirty injectors. About a year ago, shortly after the last post, I tried one bottle of Gumout Complete Fuel System Cleaner with PEA (poured 1/2 bottle for 2 tanks) and by the 1st 1/2 tank there was already a noticeable difference and when it was time to fill-up the rough / hunting idle at cold start was completely gone. I now use a bottle of Gumout Regane (entire bottle in 1 tank) at each oil change (~4 months) and by the time the next oil change comes around the idle may start to act up a little (although not near as bad as before) but after a tank with Gumout it is smooth as silk and no hunting.

I will note that up until I tried Gumout I ran a 5oz bottle of Lucas Fuel Treatment about every other tank (I buy 1gal jugs and refill the 5oz bottles) for all my cars for about the past 5 years, and all the while this Accord still had a rough / hunting idle at cold start. So for cleaning it seems PEA far out performs Lucas Fuel Treatment based on my experience here.

Now I run 1 bottle of Gumout Regane in each car at each oil change.

Hope this helps others.