strange problem in my w123 230
 

i have faced a strange problem in my w123 230 mercedes the problem is that from 2 months when i start to crank the car it work but the car is making cutting voice and the air from exhaust is cutting reguraly as if u turn it on and off quickly accompanied by shaking of the car and also noticed that there is a liquid come on the exhaust tube near the starter of the engine and evaporates but i check the liquid and found it very light not the oil engine something elseand sometimes when i start it after turning it of by 30 min it didn't start and i must press the gass pedal or crank very long to start and sometimes it start perfectly with no shock and also the liquid didn't appear except the car begin to shake. now from 2 weeks it start perfectly without problems i want to know what is the problem?