My 126 runs well on smooth surfaces but vibrates when on rough. It vibrates more than usual but real smooth if the road's good. I changed all the front bushings and had the wheels balanced. I thought it could have been the drive shaft but am now thinking that its just normal.
One way to find out if your engine mountings need replacing is to step on the brake with the engine on, and engage into D or R and feel the vibes. If it vibrates badly, then perhaps the mounts have to go.
126 tailed by a 203, 129 leading the pack.