Why does the RPM bounces goes up and down at a stop?

Question

i got a 99 civic si. when im driving everything is fine. but when i make a stop and leave the car on the RPM moves up and down betwen 0 and 2.

Answer 1

Erratic idle is the classic symptom for a vacuum leak.  From where?  Who knows.  Finding it is the fun part.

Answer 2

Could be a bad tach or bad connection in the wiring to tach. If the engine rpm,s is going up and down with the tach,then it could be a bad idle control valve. possibly a bad ignition ignitor.

Answer 3

its starving for gas, your fuel filter is slightly clogged, the fuel pump is building up pressure and when it hits a certian pressure , fuel surges thru the filter and delivers a gush of pressure to the carb-injecters. then the pressure returns to a low state and this is what causes the jump in rpm's.