jetta stumbles on acelleration

i have a 94 jetta gl that in the past few day has been stublimg really bad on acceloration in every gear. i think it could be due to the fact that i just changed the spark plugs, but what happened was that the person who had the car before me didn't take very good care of it and the never replaced the plugs or wires and when i pulled the wire off the plug on the passenger side on the motor i noticed that the top of the plug ( the part the screws off the plug) came off in the wire and i cant get it out so i just replaced three out of the four plugs. it is like the timing is off. also when i rev my engine in nuetral i can hear what sounds like a piece of sheet metal that is loose or something. is it some sort of inspection plate that is loose, or is the cap and rotor making that noise. a friend of mine said that the cap and rotor can make that kind of noise when they are worn out. thanks for all the help

Gotta get that 4th plug out. Also replace the wires while you are at it. You are misfiring either because that plug is fouled or because whatever is stuck in the wire is not getting good contact.

I notice a metal vibration sound while accelerating my 96 gls but it goes away when the engine is warm I don't pay it much mind probably just a plate on the converter or something. If you are tuning the car up you should replace the cap and rotor. That is an important part of the car running right if at all.

Hope that helps