Honda Idle Issues, Hunting Idle

I get flooded with questions about Honda idle issues so I’ve put together this article to address these concerns. This article is for a hunting or erratic idle, the original idle speech was for a ‘shaking’ or ‘rough’ idle. For that, check out the other link about Honda idle issues.

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Step 1, check for air in the cooling system. This is the most common cause of an idle issue on Honda’s. Especially if you just serviced the cooling system. And by service the cooling system I mean replaced a radiator, water pump, thermostat, radiator hose, head gasket, anything where you open the cooling system to replace a part. You MUST follow the procedure outlined in the video. It’s not important that you have a bleeder valve as those are really only there to make filling the system easier. You can skip that part if you don’t have a bleeder screw but you MUST follow the rest of the procedure to the letter in order to ensure

you’ve bled all the air out. If you fail to bleed all the air out, the idle issues will continue. If you find that the problem goes away after you bleed the air out of the cooling system but it comes back a few days later then check for a leak in the cooling system using the second video on checking for an overheat condition.

Next, check for vacuum leaks. Vacuum leaks are the #2 cause of Honda idle problems. In fact I would say that all Honda idle problems are mixture related and vacuum leaks can be a big upset to the mixture at idle. Vacuum leaks add too much air to the mixture causing the engine to run lean. The computer also fights them as it tries to maintain an idle using the IAC but it can’t keep up so you get a ‘hunting’ idle condition meaning that the idle fluctuates from high to low and it never levels out. This condition is often worse after the engine warms up. When cold you just get an idle that is too high like up around the 1200-1500rpm range or higher. The second video shows a vacuum leak that I found on a Civic using a ‘safer’ method for checking for vacuum leaks. Both work but the important thing is that you check for vacuum leaks if you have a Honda idle problem. My bet is that you’ll have the problem solved in these first 2 steps.

If you’re sure you don’t have any vacuum leaks, and you’ve bled the air out of the cooling system, and you still have a problem, then check the IAC (Idle Air Control valve). You can do this by tapping on it with the butt of a screwdriver while the engine is running. If the idle changes or stumbles in some way you may need to replace it. Many people try to clean them with mixed results. In short, cleaning may not be the answer, you may need to replace it. Personally if I find a problem with one I just replace it. Cleaning CAN work if the pintle is getting bound up in some way but if the valve is having an electrical issue then you’re going to have to replace it no matter what. Cleaning won’t help. I should also mention that it could also be a connection or wiring issue so don’t forget to check those as well if you find the IAC to be the cause of the idle problem. BTW the Honda J series V6 engines from about 99-2004 are famous for IAC problems in fact, you might even see a check engine light for it. If you do it’s a good idea to check it as I’ve outlined here and replace it if you find that it’s bad.

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