The Accord has been running fine until the last three months or so when a CEL would come on intermittently then go off, then on and off. Then slowly the car began to idle extremely low, and would occasionally stall. I was unable to adjust the idle, so it idles at around 3-400RPM I am guessing.

Today I pulled 6 codes:

P0133 - O2 sensor Bank 1
P0401 - Exhaust Flow Insufficiency
P0505 - Idle Air Control Valve
P1491 - Exhaust Gas Recirculation Valve Insufficiency

These were pending?
P0401 - Exhaust Flow Insufficiency
P0505 - Idle Air Control Valve

So... Where do I start? Should I clean the EGR Valve with Carb cleaner? Do I need to clean the EGR ports? Should I wait to replace the O2 sensor?

I am unsure if the EGR valve is clogged and that is causing the O2 sensor error, or the O2 sensor is shot and is causing the EGR codes. I feel the IAC is fine, but the P0401/P1491 are confusing the IAC which in turn is causing my low idle.

Any Honda Techs have a flow sheet or shop diagram I could follow to try and diagnosis this? This car is gem here in Upstate NY, a SC car, that has only seen two winters, I have owned it since 206K miles and it has been a great car!!

Thanks Guys!!

 

Is the car idling correctly? if not, address the IAC as that could affect the O2. for the EGR problem, open the EGR valve with the car idling and the engine should stumble or stall. you will need a circuit diagram to know how to manually open it. This will tell you if your passages are clear (enough) or clogged. if the engine rpm doesn't change with EGR applied at idle, your passages are clogged or the valve isn't actually opening even though you are commanding it to.

 

The car did have a low idle issue.

I bit the bullet and went with my gut, found 5 out of 6 EGR ports completely clogged. I will post up some before and after pictures. This was actually super easy on the 2.7 Non-Vtec V6.

I also cleaned out the TB.

It took a minute to restart the car, but it eventually started. Idles fine, picks up well, only put 40 miles on it, but light remains off.

I hope that was causing ALL of the problems. I am just going to wait for now and see if any CELs re-appear.