i drive a 99 si with type r cams, and msd ignition system and coil, sometimes when i hit vtec the engine will stutter. it only happens sometimes though and completley randomly also just as randomlymy idle drops to like 200-300 when i let my car sit. i can feel the engine kinda pulse when it drops this low and the exhaust makes a kinda of put-put noise. if i turn on the fans or a/c on or drive around for a lil bit it will return to normal, but then the car seems to idle a lil bit roughly. any idea what it could be? any suggestions would be appreciated thanks. i also replaced the battery last week, and have cleaned my fuel injectors and seafoamed my engine as well. this problem has been occuring for a couple months

 

I have a 93 Si with a D16 Z6 vtec, I took my converter off of mine and it does that now. That might be your problem too. But it does not stutter when I hit vtec.

 

I set the idle speed up on mine now. When I first start it ldles at 2300 for about 45 seconds and then when it get up to normal runnning tempature it idles just fine.