The Honda Accord is known for its durability and longevity, but even the most resistant cars undergo wear, many times leading to idling problems. The Accord most often experiences a consistent shuddering when idling, which can be solved quickly by adjusting the idle screw. A more erratic idle is often caused by vacuum hose leaks or a faulty fast idle thermo valve. You can save yourself a trip to a garage by diagnosing your Accord's idling problem at home.
Turn the car on and let it run for five minutes, then lift the hood and locate the idle air control valve (this valve is located in the engine compartment, behind the intake manifold). Unplug the control valve's electrical connection and locate the idle screw on the throttle body. Adjust the idle screw (it is very sensitive; rotate the screw by 1/4 turns) until the car reaches 800 rpm.
Turn the car off and reconnect the control valve's electrical connection. Use a socket wrench to disconnect the battery´s negative terminal and wait five minutes. Reconnect the negative battery terminal and turn the car on -- the vehicle will idle smoothly around 650 rpm.
Check all of the vacuum hoses and seals in the engine compartment, particularly on the throttle body and intake manifold. Any leaks in the hoses or seals can cause an erratic idle, as the engine will try to compensate for the loss of air caused by the leaks. Any leaking hoses or seals must be replaced immediately.
Check the fast idle thermo valve -- remove the intake tube from the throttle body and locate the two holes on the inside of the throttle body. The bottom hole leads to the fast idle thermo valve. Once you have located this hole, start your car, let it run for five minutes and then feel for any air coming from the fast idle thermo valve opening in the throttle body. If you feel any air or suction, the fast idle thermo valve is the cause of your vehicle´s erratic idle.
