Honda Idle Issues, Hunting Idle
Lastly, don’t adjust the idle screw! This often gets done first thing and can actually mask the fix when you finally do fix the idle problem. If it looks like someone has messed with the idle adjustment screw perform the idle relearn procedure. Depending on the model you normally unplug the IAC after the engine is fully warmed up and adjust the idle screw until you reach base idle which is normally in the 700-750rpm range. This will often set a CEL so
you’ll need to reset that after you’re done. Also don’t plug the IAC back in till you shut the engine down to help protect the PCM. Consult the service manual for the vehicle you’re working on for specifics on resetting base idle.
Notice I haven’t said anything about the MAP sensor (Manifold Absolute Pressure sensor). This is not a common problem on Honda’s and once again, it’s external damage or aftermarket parts that I normally find fault with. An erratic idle CAN set a MAP sensor code, which is why I mention it. The reason for this is because the MAP is in essence a vacuum gauge so if it’s gets strange readings from a fluctuating idle it can set a MAP sensor code. It does not mean that your MAP sensor is bad however. This is not that common but I feel it’s worth mentioning because I have a lot of people say the replaced or worse yet, CLEANED the MAP sensor to correct an idle problem. Don’t clean a MAP sensor, you’ll likely ruin it if you do. If you have a CEL with a MAP sensor code and a fluctuating idle, address the idle issue first, reset the code, and see if the MAP sensor code comes back. My bet is that it won’t come back after you get the idle problem solved.
Lastly (I promise), don’t rule out a mechanical issue. If you get an idle issue after you replace the timing belt and water pump or some other cooling system service, first check for air in the cooling system, if you don’t find any, check the mechanical timing. If you’re off a tooth with your belt it is possible that will cause an idle problem. In addition, if the engine has bad valves or a compression problem this can also cause an idle issue. I would check all of the above suggestions first, but don’t rule out a mechanical problem when diagnosing a hunting idle on your Honda. If the engine isn’t working properly then it can cause all kinds of other problems, not to mention idle problems.
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