My 99 civic is dies when it reach to normal temp. It seem like too much gas in getting dumped into cylinders. Can someone tells me what controls fuel & air mix into cylinder?

 

your ecu which uses the o2 sensor to read the mixture and make sure that it is right.

 

It's even more complex than that. The O2 sensor is only one important input -- MAP, ECT, TPS, IAT, distributor sensors, CKF, KS, and VSS are just some of the other ECU inputs used to determine optimal air/fuel ratios.