Sharan 1.9tdi 1998 starting and power loose when engine gets normal temp

I have start to feel that the engine whodnt start at first movment of the key,day by day i ve felt that was takin more and more time to start,first even hot (electrician discovered that the tube that gives information to the electronic was damage,problem soved)and now i got serious problems to start in cold 10 to16 degrees celsius sometimes I need 10 seconds or more to start and when it starts it makes a lot of smoke too.sometimes it starts in 2 cilinders,(at list thats what I feel) oil and batt. blinks at same time engine starts like that.I ve felt too when it gets to normal temp it loose power.Ive both it 1 month ago I know I got warranty but Im scared of the seller because hes got air that he will fool me.Elelctrician told me that in the pump there is some electric valve that is inside an is very usually that kind of pump gets that problem. Is that true? He also put a air mass measure for 3 or 4 days bu the problem is the same.I shold tell you that when I both it, the oil level was in the midle and Ive put some more than max 4 milimeters more or less .is that a big problem? please Help me Im geting crazy Please.P.S. seller has show me the paper wher he told me that he shanged the 4 injectors and starting plugs too,after starts and driving it doesent make any kind of smoke