I have a 1999 Honda Civic DX Hatch. It has a built GSR Motor. The car has been running fine for a long time. Recently I went to turn it on and it started but will not idle on its own. If i let go of the gas it will just die. What could cause this?

 

Too many things to list.
Start by telling us what engine management the car is on, what map sensor & if the car is throwing any codes (check engine light).

 

I have Hondata s300, omni power 4 bar map senser, and the car is not throeing any codes

 

you can start by using the search feature and searching for threads on "IAC" and "LOW IDLE" etc..

It's much easier to help someone if they've tried a few things first.

When you get the car running with the throttle is it smooth and running good?