Hello, with an intermittent rough idle, there are a few different things that can cause this. The first would be to check the throttle plates for any carbon build up around the edges that can cause the plates to stick sometimes. With this high mileage it would be good to clean them. A cylinder with a slight misfire that's not contributing as much as the other cylinders will cause a rough idle, especially on a 4-cylinder engine. Hondas are one of the few that require a valve adjustment as regular maintenance. Fortunately, it's pretty easy to do on these once the valve cover is removed. If they are not adjusted every 30,000 miles or so, the valves can become too tight or too loose, causing the valves to either stay open slightly or not open enough. I'll post information on adjusting them. They can cause the engine to run differently when warmed up vs cold. This vehicle also has a Idle air control valve that allows extra air into the engine during cold start, that plus dirty throttle plates can cause cold running issues.
There are also some fuel treatments you can add to the gas tank when filling it up that will help to clean out the fuel injectors. With 200,000 I would recommend doing all these, it will really help the rough running, and help the gas mileage.
Has the check engine light been on at all?
And how did the spark plugs look when you took the old ones out? Were they carboned up at all, or more of a whitest color?
The valve adjustment may sound intimidating, but when you've done it once you'll see it's actually very easy. and I guarantee when you go to check them, you will find that some of the valve clearances are very tight, and you won't even be able to get a feeler gauge in between the valve stem (end of the valve) and the rocker arm. Especially on the exhaust valves. I have found that every single one I've done has needed adjustment. There is even a tool you can buy that is very cheap to help adjust them on Hondas, Ill post a picture of that as well.
Here is all the information on the Idle air control valve (IAC), the throttle plates, with a wiring diagram to show the wire colors for the IAC valve.
Then each step for adjusting the valves once the valve cover is removed. If you have any questions about any of it, just post them here.
https://www.2carpros.com/articles/idle-air-control-valve-service
https://www.2carpros.com/articles/engine-misfires-or-runs-rough
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Tuesday, October 24th, 2023 AT 8:14 AM
