Brian4200

I brought a 01 civic about a week ago runs and drive great no power loss no hesitation when stepping on the gas. the problem is when the car gose from high idle down to resting it runs a little ruff but stays at 750 rpms it will drop down below 750 when you come to a stop almost die then kick back up to 750 rpms i have cleaned the IAC and the egr done a basic vacuum check no hissing sounds from the engine but one weird thing is if i pump my breaks the car will smooth out then if i stop pumping the car will idle worst then before i have takin the vacuum hose off the break booster and plugged it no change in idle also has brand new ignition coils and new ngk plugs

Colin42

To me the fact that pumping the brakes smoothes out the idle points to a vacuum issue, try spraying brake clean around the intake, throttle and any vacuum lines, if the idle changes you've found a problem.

ezone

Got any fault codes?
Battery disconnect, then do an idle relearn?

Is it a vibration---- or is it a rattle caused by vibration? Hood rattles can get pretty loud at certain rpms, so do exhaust rattles
Aftermarket motor mounts are usually harsher (transmit more engine vibration than oem mounts)
the engine is just a 4 cylinder, they shake at low rpm anyway

Pumping the brake can cause enough rpm change to make the complaint go away, and i bet holding the gas pedal down very slightly will too

Brian4200

It had missfire codes for cylinder 3 and 4 when i got it but i changed the ignition coils and plugs that went away. The engine lopes when idle and shakes the car and dips down to 300 rpms or so when coming to a stop and when the idle gose from high to resting and it will die sometimes but starts right back up I have tired all the stuff from this forum except the pcv valve and fuel filter which im going to do this weekend. Rpms do not hunt it sit at 750 pretty steady