I have a 99 ex with light mods done i.e. intake, full exhaust, external coil, msd cap/rotor. I've had all this on for a while now but, the car seems to have a studdering/hesitation at lower rpms all the sudden. While I drive and at low rpms, the car will studder, and at idle it happens too. If i give it some gas at idle, it hesitates then revs up. I changed the plugs yesterday and the fuel filter a couple months sgo. Any ideas on what is wrong with this thing?¿?

 

get rid of ALL that msd crap for OEM, thats probably your issue. Put the OEM intake back on for sure, thats also your issue. get the OEM cat converter back on, and then check for exhaust leaks.

After all that then make sure your timing is correct, check fuel pressure, then make sure your fuel pump is working correctly.

check the ecu harness for breaks and shorts