I just finished fixing the P0401 EGR passage issue.

I put everything back together. Started the engine and everything seems fine.
So i took it for a test drive and all was well.

I stopped to get gas and when i put the car in park, the engine started to rev up then go back to normal, over and over... about 650 RPM to 1500RPM.

When I drove it home, SEL came on and P1129 MAP sensor value more than expected.

I checked that I put the vacuum hoses back and it all looks good.

Any ideas?

 

You may have switched the connectors for the TP sensor and the MAP sensor.

The connector to the MAP sensor should have a Yel/Red wire, a Red/Grn wire, and a Grn/Wht wire.

 

The connectors are in the right place.

Just a question. I liberally used throttle cleaner on the trottle body.
Is it possible the solvent may have damaged the MAP sensor or the idle control valve?
I may have even got some solvent in the intake/outtake where the coolant goes

 

I don't know if this information helps, but when the engine is cool - it idles fine.
When the engine is hot, then the idle surges and drops, over and over. 650RPM - 1500RPM.

I am sure, all the vacuum hoses are fine. Only 4 things I can think of:

1) maybe the upper plenum gasket got a kink in it. I did have trouble putting the top on and the gasket got bent a bit. I was able to straighten it up.

2) The other is the idle control valve - maybe when i was cleaning it with throttle cleaner, some of the gunk got in there?

3) I also took the EGR valve off, to clean the ERG passage. Mayeb the ERG valve has an issue?

4) I read online about air pockets in the coolant line that goes to the idle control valve. Not sure how I can check this, without taking the top part of the throttle body off again to get to the coolant tubes.


Still- the bottom line is engine cold- idle is fine.
Engine hot,- idle surges up and down.

Any suggestions?

 

Sounds like air in the cooling system. The upper intake does have coolant running through it, so you probably introduced air in there. I think the 1998 and newer accords did not have a bleeder valve on the throttle body. If that is the case, then remove the radiator cap when the engine is cold to allow air to bleed out of the system. There is an ericthecarguy video on this procedure.

Air in the cooling system shouldn't give you that code. Please verify that the map sensor wire colors are yel/red, grn/wht, and red/grn. You can easily switch the connector with the throttle position sensor.

 

The connectors are in the right place. I took a picture before taking everything apart. Gray connector to MAP, blue connector to the TP sensor.

I will try the bleeding trick. I did that yesterday, but did not turn on the heater or remove the radiator cap while doing this. Will try again when i go out later this morning.

If this does not work, does a vacuum leak cause surging? I would think if there was a leak, the extra air would simply make the engine run at higher idle and maintain high idle.

Otherwise, I guess I need to take it back off again and check all hoses.

 

SOLUTION: Bleed the air out of the coolant.

I don't know why it didn't work yesterday, but I let the engine get hot- loosened up the bleeder and within 1-2 seconds, the engine settled down.
I don't remember, but it's possible I didn't let the engine get hot enough yesterday when I bled it.

Thanks again for pointing this out!

 

I'm glad it worked out.

Thanks for posting the solution, because it will help others in the future when they read this thread.