I have a 1993 5.0 with the 5 speed manual. Under acceleration, sometimes the whole car vibrates fairly severely (with the RPMs) when in gear, but other times will take off as smooth as can be. It is only really noticeable in the first 3 gears. I have noticed that when the car has decided to vibrate, it continues to vibrate even when I push the clutch pedal in, but stops vibrating if I coast in neutral with the clutch pedal out. I have also noticed that the car has a tendency to decide to accelerate smoothly when I slip the clutch a lot taking off from a stop, but this does not always work.
I'm not sure if this is related to that problem, but sometimes the trans also takes a lot more force than normal to put into first gear from a stop (but shifts through all other gears normally), and other times shifts into first very easily.
I do not hear any unusual noises.
I also am led to believe that it is not any of the motor or trans mounts because I replaced all of those with polyurethane units a few months ago and none of the bolts are loose. The car only very recently developed the problem with the vibration.
I'm not sure if this is related to that problem, but sometimes the trans also takes a lot more force than normal to put into first gear from a stop (but shifts through all other gears normally), and other times shifts into first very easily.
I do not hear any unusual noises.
I also am led to believe that it is not any of the motor or trans mounts because I replaced all of those with polyurethane units a few months ago and none of the bolts are loose. The car only very recently developed the problem with the vibration.