Low idle at stop lights with A/C on

DBOYZ

MEMBER
2000 HONDA CIVIC
1.6L
4 CYL
2WD
AUTOMATIC
180 MILES

With engine fully warmed up and in park A/C turned on high idle is smooth. Put it in gear the idle stays smooth, but when driving and I come a stop engines idles down low to about 600 rpm's. Everything else checks out great! Could an over charged A/C system be the cause?

1 Reply

JACOBANDNICKOLAS

MECHANIC
108,170 POSTS

Hi,

No, the A/C isn't the issue. When you turn the A/C on, do you hear the engine idle speed change? I ask because the idle speed is controlled by what is called an idle air control valve (IAC) and should react to different loads on the engine to maintain idle speed.

I attached a pic of the IAC location for you. Now, the IAC could simply be failing or dirty preventing the proper amount of air to enter the engine. Here is a link that explains how to service one. Try this first.

https://www.2carpros.com/articles/idle-air-control-valve-service

When you remove it, make sure there is no carbon built up into the throttle body as well.

Keep in mind, a common cause of a low idle can also be related to an engine vacuum leak, but based on your description (works normally until driven) I doubt that is the issue. You may also simply need to service the throttle body. I will include a link for that as well if you want to do it.

https://www.2carpros.com/articles/idle-air-control-valve-service

Let me know if you have questions or need help. Also, let me know if this helps.

Take care,
Joe

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