Thanks for the reply. Could it be the cooling system also? My girlfriend's sister had mentioned that during her service at Sears a few months ago, they recommended that the coolant and such be flushed and replaced. The mechanic I spoke to today said that it is possible that air stuck in the system may cause the surging idle. Would air in the cooling system cause a vacuum leak? I am planning on having the mechanic flush and bleed the coolant if necessary and also clean the throttle body and check whether the IAC valve may be cloggedsince it's right underneath.

As for the EGR, she did get a new EGR valve. I would assume they did the port cleaning while replacing the valve? Could a bad gasket be the culprit? I'm just trying to get this solved starting with the cheaper, more easily overlooked things.

 

i hear ya...cheaper is always better.

low coolant or air pockets can cause idle problems. that valve uses coolant temperature to lower the idle. if there is a coolant problem the part of the valve that does it's part in lowing the idle will not do so, and the car will surge because the only way to lower the idle is to cut the fuel, then to keep the car running it turns the injectors back on, then cuts the injectors off again as the idle becomes uncontrollable, and repeat.

SO! we know it can be a multitude of problems. to check for a vacuum leak from sources such as intake or throttle body gaskets and vacuum hoses, go buy a can of throttle cleaner and spray it around the throttle body and suspect vacuum hoses. if the idle speed changes or revs when you spray a certain found you found a problem!

 

Replaced the IACV on my 2001 Accord V4 because of startling engine on the cold start, but no OBD codes. Got a direct replacement from Advance Autoparts. Replaced it. A day after P0505 came on. Go figure. Checked all the vac lines, checked the connector. All seem ok. Do I need to adjust the idle speed, replace the coolant, or just trash the replacement valve?

 

First check everything out like vacuum leaks, bleeding air from cooling system, etc.

Do this procedure for setting the base idle, then re-learning the idle.
https://www.hondaaccordforum.com/for...e-speed-38734/

 

Ok. Thank you. So, it sounds like, I have to do Idle speed adjust. Not sure, if I could do it without a Tach. May be I'd better take to the shope for that, assuming the valve is ok.

 

You can probably get away without a tach. The tach in the cluster isn't very outstanding down there, and the markings are kinda funny. Almost like its missing a mark at zero, I'm trying to remember the details. Maybe someone's got a picture.

If you don't have an external tach, give it a shot anyway. 550rpm is pretty low, but you can get it to idle there.

 

Jim,

Thanks a lot for the info. Just an FYI. I usually do lots of highway driving. About 1.5 hrs each way. So, yesterday. I thought, I'd go back, let the car fully warm up along the way, do the warm adjustment by feeling the RPM-gage, let it completely cool off over night, and do the ECU reset in the morning. About 45 min into my drive the indicator went out..... I checked, the bulb did not burn out . The RPM's still seemed a little high, but the engine seemed to be a little more settled. So, I thought, I'd change the procedure a little, since there is no active OBD code in the unit. So, when I got there, I turned all the accessories off and adjusted the throttle to abt 750 somewhere warm, where I think, I had it before I replaced the IACV. In the morning, I turned it on, waited to the full warm up without touching the pedals, went back out on highway. The indicator is still out. While on the highway, I noticed, that my RPMS seem a little too low, and acceleration seemed a little too choked. So I pulled over and turned the screw back open by another 1/4 turn. That is where, I think, the engine started finding its happy place. The accel and running seemed pretty smooth. Got to my destination. And the indicator is still out. Will keep you posted, if anything changes. But for now, all seem fine.

I think, about 1.5 years ago I did the idle speed adjustment, which probably compensated for the reduced flow through the IACV. Now that I replaced it, I noticed that my RPMS seemed a little on high side compared to before. So, I probably just had to adjust back. And I think, in most of the threads I have seen on replacing the IACV this one aspect was missing. None of them seem to mention the idle speed adjustment post replacement.

Thanks again

 

Well, the one thing it all hinges on, is if you try to adjust the idle while the IACV is plugged in & working, then the ECU will compensate against your adjustments. So you can reach a point where you have changed your base idle a lot but don't realize it.

Remember, BASE idle is with the IACV unplugged. Operating idle is the normal everyday idle, with the control system active & working.

 

Good point. I think, I altimately went somewhere abouts one full turn back on the throttle screw. It seems to be runnig fine for now and without any codes. But you are right, I should probably go back and do it right over the weekend.

On the side note. Any guess on why did the code disapear on me by itself? A bubble that finaly vented out somwhere or the RPMS went temporarily back into the range at higher highway speeds? I would be curious to find out. Thanks

 

I'm not sure the real programming details, but I suspect that if the ECU needs to command the IACV to go too far open or too far closed, that triggers the code. You probably adjusted it close enough so the IACV is operating somewhere near where it wants to be.

Think of it this way...
As you turn the idle-air screw the ECU will command the IACV to open or close and compensate, trying to hold the operating idle at 750. So you turn the screw some but it doesn't change the operating idle. Then you keep turning that screw until the IACV runs out of range, and then the operating idle actually changes. I suppose you have gotten it somewhere back into range.