hey im buyin a car for my gf i found wat i think is a good deal a 1994 dihatsue appluase with 140,000 ks and in good condition pwr steering automatic air con. My only problem is that the engine vibrates significantly when in gear and in idle. The vibration goes away once u accelarate in gear or when the car is in nuetral. My theory is once u put it into gear (drive) the transmition engages the motor putting stress on it thus lowering the RPMs cuaseing the motor to vibrate as it is idling too low. My question is what exactly is going on in the gear box to cause the vibrations (as i have little idea of how a automatic works). I know to an extent this is normal as several of my bikes and do something very simmilar. I want to know what is wearing out in the gearbox and how much would i pay to replace it (i know reebuild is about $800) but more importantly how long u can leave this unchecked without doing anything.