Correction from yesterdays question. My KIA optima 2004 engine vibrates at low RPMs, but when it runs over 2000 rpm, it runs smooth.
There could be a problem with one of the engine mounts. If they are bent or the material inside of the mount is faulty it can cause vibration at low RPMs.
engine mount,tranny mount,or jumped time.
try your balance shaft belt. look under timing belt.... also do your timing belt and water pump while your there...
may be problem with ignition sensor faulty singal at low rpm
may be faulty ignition sensor, falty signal at low rpm
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