I just bought a 00 Si about 2 weeks ago. I changed the oil, and the plugs. About two days later the car started sputtering at idle (stop lights, stop signs, before parking). Almost dying but not quite. It also seems to hesitate throughout every gear at just about any rpm. Nothing heavy but I noticed a slight (<100 rpms) dip in the rpms when it happens. Also when I let off the gas in any gear (approaching speed zones preping for a stop) she backfires but not quite. More of a bubbling in the header/cat area.
SO....
I changed the plugs and wires again, checked the PCV valve, checked the IAC and adjusted it a bit to no avail. Oil is clean as a whistle (thank god), plugs are gapped .05 of an inch as specified in the owners manual. I used mid-grade for one tank til i noticed premium only notice on the cap (d'oh!). Ran fuel injector cleaner through it. Checked the ecu for any flashing of lights, nothing. The kid I bought it off said he changed the distributor about 1 1/2 months ago. The only thing I can think of is fuel filter? Any guesses? Oh and by the way she's only got 69k on her.

 

pull the dist. cap off and check the rotor...also check the ignitor(internal coil) for hot spots very common for them to go bad

 

I would suggest checking the IGNITION TIMING and the CAM TIMING.

 

Actually it all came down to the previous owner put one of them venom chip in it. The wiring looked fine but my friend yanked one wire out of there and it idled like a champ!!

THANK GOD FOR GSIR!!!