Very specific idle problem – 2000 Honda Accord 2.3

[Y]

Hi guys,

I was just wondering if any of you idle experts can figure this one out or at least narrow it down for me. I’ve been trying to figure it out for a while and I have limited equipment and no garage so I can’t be taking everything apart.

After driving for about 10 mins (after engine warms up), I get this intermittent idle problem (in neutral – manual) where every 2 seconds the idle drops a bit and I can feel the whole car shake momentarily as if it wants to stall but it doesn’t. It’s periodic and not random. I have a code for EVAP system p1457 but I don’t think that’s the problem.

Since it was periodic like that, I thought it could have been the IACV. If I unplug the IACV the engine speeds up but there is still a periodic fluctuation. If I plug the IACV back in but open the throttle to about the same RPM, the problem is gone and it’s pretty smooth.

Also, when I unplugged the IACV (throttle closed), I do remember hearing a hissing sound but that may have just been air rushing through the IACV port.

Would a bad EVAP purge valve be causing that? I wanted to test it but had a hard time getting the vacuum hoses off. Could it also be the EGR stuck open or a bad TPS?
The main thing that confuses me is that the engine was varying periodically and was still doing that even when the IACV was unplugged but then it was fine when throttle opened.

I’ve also noticed that occasionally while revving the engine in neutral, when releasing the accelerator, the RPM drop pauses a bit somewhere on the way down before fully dropping to idle. I don’t know if that’s related.

Thanks.

Topic

[college man]

Usually when you unplug the IAC the motor should stumble.

https://ericthecarguy.com/kunena/8-Service-and-Repair-Questions-Answered-Here/41476-solving-honda-idle-issues-hunting-idle

https://ericthecarguy.com/kunena/8-Service-and-Repair-Questions-Answered-Here/41475-solving-honda-idle-issues-rough-idle

[Y]

Yeah, I read those threads but still couldn’t really figure it out.

What do you mean by stumble?
Mine kinda does something similar to this when I unplug the IACV (after 50s mark):
http://www.youtube.com/watch?v=WEbsgLrLEwk

I guess i’ll keep trying different things until I get it.

[Author]

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