i think inherent na sa 4ja1 ung malakas ang vibrations as per my experience with 4ja1 for 3 years. during cold starts, A/C on. pero hindi naman masyado vibrating at high speeds na. from my point of view, dahil siguro sa timing gear sya e nagkakaroon ng torque reversal from the constant meshing of gears. just my opinion.
pero among the diesels i have driven, saludo pa rin ako sa 4ja1. matibay, matipid kahit mahina sa acceleration. namaneho ko na rin kahit nabali na pala yung isang valve at ayaw nang lumampas ng 30 km/h.