i have a 99 Si(US ex) i have a big exhuast leak where the header and the catayltic converter meet could this codes be caused by that or what else is causing these codes?

Codes:
P0171
1. Fuel Metering Too Lean
2. Fuel System Too Lean ( Right bank (bank 1)
3. Rear bank (bank1) Fuel System Too Lean

P0131
1. HO2S (B1) S1 Circuit Low voltage
2. HO2S (B1) S1 Low voltage
3. O2S (HO2S) (S1) Voltage Low

P0303
Misfire No3 Cyclinder

P0304
Misfire No 4 Cylinder

P0300
Random Misfire

 

Does the car drive just fine or does it act up?

 

i havnt drove it i just got it but it runs fine

 

i havnt drove it i just got it but it runs fine

 

If you haven't driven the car, then you don't know that it runs fine. All of the O2 codes you have there are related to the primary O2 sensor, not the cat or secondary O2 sensor. Do you have the OEM exhaust manifold, or aftermarket? If you know there's an exhaust leak, why don't you fix it?

 

aftermarket it idles fine

 

And exactly where in your header is the primary O2 sensor installed? Near the head flange in one of the runners? Near one of the mid point collectors? Near the final collector? Near the cat flange?

 

Fix the exhaust leak and replace the spark plugs, which are likely fouled due to the engine running rich.