I have a 2000 honda civic dx with I/H/E and a y8 intake manifold. Ever since i have had the car its' idle, when cold, jumps up and down, and when warm the idle hovers when letting off the throttle. Also, the car jerks badly when the throttle is touched. In addition to all that the gas mileage has been horrible at about 22 mpg. What could be causing these issues?

 

the jump could be caused by a bad idle air control valve or a bad fast idle valve, jerky throtle i dont know, and bad gas milage may be dur to the fack that you opened up the airflow, so more air means more gas= less gas mileage