2009 Honda Accord runs rough in park

My 2009 v6 Accord slightly sputters when in park but not when stopped in drive. It has about 120K miles. Any idea why? No check engine light and RPMs are stable when it happens.

The problem could be related to whatever controls the idle rpm. On your car it is probably controlled by a computer & algorithm. The computer reads several sensors to determine the optimum idle rpm for the situation, then opens or closes the air path into the engine using an electric motor or actuator to achieve the desired idle rpm. So either one of the inputs from a sensor is wrong, or the mechanism that opens and closes the air path is sticking.

Another theory, the engine air/fuel mixture is incorrect, and for some reason this shows up most at idle in P. Ask your shop to check the idle fuel trim data. If there’s a problem with the mixture, it should show up in that test, which is easy for the shop to do.

This might be interesting to OP: Several callers on the old radio show called w/ similar problems . Caused by an air leak into the engine causing a too-lean mixture, only happened when the car was in P. Why? Those cars used automatic parking brakes, engaged by themselves when shifter was in P. Done w/vacuum actuator. Faulty actuator would create an air leak into intake manifold when shifter in P.

Have someone clean the electronic throttle body to see if that smooths the idle out.


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