One of the more common issues with used Hondas is rough idle and many things can contribute to this issue. Here are some steps to solving rough idle problems in your Honda:
When you notice idle issues, take a moment to think about the condition of your Honda. A lot of the time a good ignition tune up will smooth out the problem. Old plugs and plug wires for example, can single-handedly cause idling problems.
Check your oil level. If your Honda’s engine is low on oil, it will be overworked and run rougher. Use the proper amount and type of oil at every oil change and check the levels and color in between oil changes.
Inspect your PCV valve. Your Honda’s PCV valve shouldn't be cracked or damaged in any way. What's more, if you're looking at an after-market PCV valve that's more than a few months old, you might consider replacing it. Some of the cheaper after-market PCVs start to cause idling problems after a little bit of use.
Scan your Honda’s ECM for trouble codes that may indicate a problem. If any codes are stored in the bank, it might give you a clue about a problem with your system that would lead to idle issues. Bear in mind that any code - not just a code related to the EGR system, ignition system, etc. - can be the cause of a rough idle issue. This is because a problem can sometimes lead to the engine running in "limp" mode, which can lead to rough idle.
Aftermarket modifications commonly cause idle issues. If you have changed anything that runs off the vacuum system, a component in the valve train or other modifications, you need to check for leaks and make sure your computer is tuned for the modifications.
Check your engine mounts. A worn mount will cause a disruption in the smoothness of the operation of your engine. Check for signs of wear and tear and replace worn mounts if trouble is spotted.
These are the most common causes of Honda idle problems. If you are having trouble beyond these issues, please consult with a certified Honda mechanic.