Low idle and stalling in 2000 Honda Accord V6

[PLohr]

I've been chasing a low idle and stalling problem in a 2000 Honda Accord V6. Mileage is around 129k.

It idles around 570 RPMs. Idle speed per the factory service manual should be 680 RPMs.

Observations:

• Like I said, idle is low.
• It will idle for a while after a cold start then eventually stall.
• There are some misfires at idle.

What I've done so far:

• Valves were adjusted a while ago after valvetrain became noisy. Valvetrain is still quiet.
• Cleaned throttle body, cleaned idle air control valve passages
• Replaced idle air control valve (apparently it was not the problem)
• Spark plugs were well worn, replaced them
• Removed and inspected the underside of the EGR valve to make sure it wasn't stuck open. It was fine.
• Checked backpressure before the converter. It is fine - cold or hot, at idle and at 2500 RPMs it does not exceed 0.25 - 0.5 PSI.
• Adjusted the idle air screw temporarily per the Honda procedure. This will put the engine at 680 RPMs, it won't stall, but the idle speed goes up and down, as if this isn't the real fix. It takes 2.25 turns to put the engine at 680 RPMs. That shouldn't be, something is wrong. The vehicle had the idle air screw closed (from the factory) until I temporarily adjusted it. Just to be clear, the idle air screw has been closed (factory position) for the data logging and conditions set forth in this posting, since that's how it should be.

Data logging observations (Solus Pro scanner. Using ShopStream 26.2.0.6 on a PC.):

• Log file is attached.
• Operating in closed loop.
• ECT still pretty low - 65 degrees F. That means the idle air bypass valve is still open (and will be until 104 degrees F).
• It stalled around frame 590.
• Leading up to the stall, beginning around frame 495:
  • Injector pulse width was increased, but why?
  • Lagging that (a bit later), the MAP sensor reported more load, but why?
  • The IAC command was closing the IAC valve, probably trying to bring the RPMs back down to normal level.
  • The upstream oxygen sensor was showing lean.

What's left to check:

• Coils. It has coil on plug (COP) ignition. Three were replaced several years ago, three are OE.
  • I don't have a scope to test them.
  • I don't see Mode $06 parameters that are helpful with misfires.
  • The list of Mode $06 parameters for this vehicle is attached. I didn't see anything about misfires in there.
• Map sensor?
• ???

Thank you for any help.