2001 Honda Civic warm idol rpm is low(500rpm)with some resulting vibration, simply pressing on the accelerator pedal to increase rpm to 700 or so causes the vibration to disappear....otherwise runs great. How can I increase the idol rpm? I am a do-it yourself person.

Fuel to air ratio is bad

I think the idle, in gear, should be about 750 rpm, definitely not 900. If you are looking at the tachometer, it isn't that accurate visually. a scanner should be connected to get an accurate reading. A little vibration at idle is not abnormal. But you might try adjusting the engine mounts to eliminate it.

Incorrect spark plug gap sub grade fuel plugged fuel filter emissions faulty electrical problem need more information

IF you have changed the air intake system then you interfere with the air velocity that the sensor reads to judge how much air is required by the engine You will probably experiencing other problems as well such as poor fuel economy and lack of power at certain revs.. If you want to use the mods you have made you may have to have the chip reprogrammed

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There appears to be a thermal movement of choke mechanism that comes about once vehicle is warmed up. Check the chock connections, hot water pipe and linkages tight or clear.
gazakat

check for vacuum leak

check your throttle cable or most of the times its your o2 sensor remove it while the car is on and it should stop so replace them

i'am no expert on this car, but i would chk. the T.P.S. (throutle positioning sensor) there also may be carbon build up on throutle butterfly, not letting it close completely when you take your foot off the pedel.

It is probably your Motor Mounts. They attach the engine in 4 places to the frame of the car. When the rubber wears out, it will cause excessive veibration.

Take it to your mechanic and tell him to check the motor mounts. For the front and side three mounts, it will probably run about $550 with the parts, im guessing.