Hello,

This is my first post to this forum (actually, I'm reposting it from the General Tech forum), and I am doing it for a friend. Lately, her civic's (1997 LX) engine has been surging at idle speeds. It goes from about 800 to 2000 rpm when she is in neutral (manual tranny). But there is no ill effects when she is using the accelerator in regular driving.

She took it to Autozone and they told her that the ECU was showing a code of P0240. Can anyone tell me what that code means? Or is there some place that can look it up?

Based on what I know from other cars, it sounds like a vacum hose might be bad. Are there any hoses that are praticularly proned to breaking? Or is there a component/sensor that is known for going out?

Eric

 

UPDATE: I went out to her car and heard it for myself. The idle steadily works its way up to 2000rpm then drops abruptly to 800 (then repeats itself). I unplugged what looks like the Mass Airflow Sensor (black thing, mounted with two screws to the firewall side of the throttlebody), and the idle immediately evened out. Afer plugging the sensor back in, it would continue to run well until I restart the engine. Then all the problems come back in full glory.

Any suggestions?

 

electric air control valve/idle air control valve. this is most likely the the sensor you unplugged. this sensor controls your idle. when this sensor goes bad or becomes dirty/sticky it can cause an up and down idle. the problem itself does not occur above idle speeds because it will only control idle. remove the sensor and clean it out thoroughly with carb cleaner or another good cleaner of sorts. re-install it and see what happens. if this doesnt work i would replace it.