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Discussion Starter #1
Looking for some assitance here after reading alot of posts.
2000 EX all original. Have cleaned EGR ports and changed O2 sensor at 100k. Always have Po420 code on and like many cannot get rid of it.

Now at 160k, running great but, my miles per gallon is less than 15.--I plan on running this car to 400k.

Question: Should I change the EGR and aftermarket CAT. Will this make a difference in miles per gallon? This all came up because the car suddenly stalled at idle several times yesterday just after starting up. Increasing RPM when starting seems to have stopped the problem temporarily. Stalled again this morning in park and idle.
Thanks for your assistance
A lifetime Volvo owner ~ Now Honda or nothing!
 

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I would imagine the Cat could make a significant difference in mileage as it impacts the O2 levels after the cat. Does Honda use an O2 sensor after the cat like Subaru?

Also dropping mileage can many times mean the torque converter clutch is starting to fail and slip which would cause the decrease in mileage.
 

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tmonter said:
Does Honda use an O2 sensor after the cat like Subaru?
All OBD2 vehicles (1996 and up) use two 02 sensors. That is the only way the ecu can monitor the cats efficiency.

A plugged cat can cause the symptoms you have described.
http://www.aa1car.com/library/converter.htm

Do you have any other CEL's, if you have a constant P0420 then you should either replace the cat, or run a test pipe and with spark plug fowlers on the rear 02 to trick the ecu.
 

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Discussion Starter #5
I have had a consistent P0420 code for the past 60k miles.
New Dad is there an easy way to check IAC?- I believe it is located under the throttle body ?
 

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You don't state what type of driving you do. 15 is good for the Odyssey in city driving, poor if mostly highway driving. Your CEL light is on all the time because of the Cat code. You need to check the PCM with a scanner for other codes. Also the state of the O2 sensers and cat can be determined. As stated a blocked Cat can cause lower mileage but I haven't seen any blocked cats in the new ones. Pre OBDII Cats had a ball in the middle with all the wires attached to it and when the wires burned up the ball would either bounce around or get stuck in the exhzust and block the flow. The first step that needs to be done is to pull all the codes, history codes, temporary codes, and do full analysis of the PCM data with an OBDII scanner.
 

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http://www.in.honda.com/Rjanisis/pubs/SB/A03-073.PDF P0420

http://www.in.honda.com/Rjanisis/pubs/SB/A04-007.PDF IAC Valve

http://www.odyclub.com/forums/attachment.php?s=&postid=306086 Item #2 is the IAC Valve and is located under the throttle body.

DTC P0505: Malfunction in Idle Control System

NOTE: If DTC P1519 is stored at same time as DTC P0505, troubleshoot DTC P1519 first, then recheck for DTC P0505.

1. Start the engine. Hold the engine at 3,000 rpm with no load (in Park or neutral) until the radiator fan comes on.

2. Check the engine speed at idle with no-load conditions: headlights, blower fan, rear window defogger, radiator fan, and air conditioner are not operating.

Is the engine running at 730 +-50 rpm?
YES - Intermittent failure, system is OK at this time.
NO - If the idle speed is less than 680 rpm, go to step 3; if it’s 780 rpm or higher, go to step 4.

3. Disconnect the IAC valve 3P connector.

Does the engine speed increase or f luctuate?
YES - Adjust the idle speed. If the idle speed will not adjust properly, clean the passage in the throttle body, and then adjust it again.
NO - Replace the IAC valve.

4. Turn the ignition switch OFF.

5. Remove the intake air duct from the throttle body.

6. Start the engine, and let it idle.

7. Put your fingers on the lower port (A) in the throttle body.

Does the engine speed drop?
YES - Check the idle speed. If it’s out of specification, replace the IAC valve.
NO - Check for vacuum leaks with the throttle valve completely closed, and repair as needed.
 
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