2009 Accord Idle Nearly Stalls, only in Drive, not P or N
 

My 2009 Accord 4 cyl, automatic has recently starting nearly dying on me at stoplights. It appears to be semi-random, and not directly connected to anything I'm doing (like hitting the throttle).

Symptoms: The car idles solidly at about 700 rpm, sounds fine. If the car is in Park or neutral, it will idle like this all day long with no problems.

If, however, the car is in Drive, the idle will occasionally dip down to about 500 or so, and nearly stall, shuddering the whole car. This appears to happen about once per minute while it's idling in drive.

I am not sure, but I spent 5 minutes video-ing the behavior this morning, and it appears to be connected to when the cooling fans kick on. When the cooling fans kick on, the headlights dim a little, and a few seconds later, the idle drops and it nearly stalls. It doesn't happen every time, but seems to happen at least every 3rd, 4th, or 5th time.

In all other driving conditions, the car seems fine, although perhaps a bit lacking in power on acceleration -- though I could be just imagining that. I don't get any surging at idle in drive or park, nor any strange changes in revving while driving.

I first noticed this after getting an oil change and the attendant noted they'd topped off the coolant for me. My first guess was that maybe they'd introduced some air into the coolant system somehow, so I ordered a spill-proof funnel and bled the system via the radiator cap/funnel for 20 minutes or so. Car was hot and heat was on high. I never noticed any air coming out, but I couldn't see it the entire time. Coolant level is fine. Either way, that hasn't helped, though it's possible I didn't actually bleed out any air, I suppose.

I'm guessing I should try another bleed. Is my next suspect after this the idle air control valve?

I'm not sure why there would be a difference between the behavior in drive versus park, but it's definitely there. Hopefully I can get the video uploaded and I'll append the link to this in case anyone's interested.

Forgot model/trim details:


Year/Model
2009 Accord Sedan.

Trim
5 Speed Automatic EX w/Leather & Navigation
In-line 4 cylinder engine. 2354 cc

Here's a link to a video. With the volume up high, you can hear what's going on. First stall is 33 sec in, next at 1:15, in the middle, with car in park, no stalls, then at the end, back in drive, stalls start again.

Further testing confirms this only happens when climate control is on. Since, in this weather, this means the heater should be running, I'm not sure whether this is a result of the AC compressor coming on or what, but it's definitely directly related to the climate control kicking in when.

Its hard to say exactly what is going on. It looks like the extra load on the system when the cooling fans turn on cause a drop in rpm and the idle air control valve opens to compensate.

I'd suggest to start off with the simple stuff. Check the air filter and replace if it looks dirty or is due. Clean the connections to the battery and the battery posts. Use a wire brush or sand paper.

After that, I'd stop by a parts store and have them test the battery and alternator. Also have them scan for codes to be thorough. Post the actual code(s) on here, if you have any.