ok so i added some mods to my hd.. cold air, single blade throttle body, upper plenum, exhaust(no cats but o2 still in place), msd coils...when im stationary but set in drive my engine is sputtering and the odd time it does it while WOT, everything was working mint before these mods were done.. is it the fuel/air?? coils? all i know is that i need to have this fixed before i put the pulleys on and slap it on the dyno... oh ya and my exhaust reaks like burning plastic.. its a full bassani stainless... is that just stuff burning off the pipes? lots of black sut in the pipes aswell.. I need to get this fixed PLEASE HELP ME EVERYONE thank you

 

Had similar problem with a 98 mustang gt. Did alot of work then suddenly had problems here and there. You might want to take it to a tune shop! ASAP they can also do a diagnostic check out if their is any prob~

 

What plugs are you running?

My truck was doing the same thing after I had the bottom end rebuilt. I had put in the TR6IX plugs and they ran ok for about a month and then the misfires just kept getting worse. Forget wide open, it sputtered real bad. Lived with it for so long until last week. My truck spit another plug last week and I took the opportunity to change back to the BR7EF's gapped at .038. The miss is completely gone.
Hope this helps.

 

Vacuum leak....hose left off???