maximus

I have a 98 e430 with 90k on it for the past week or so the car would not start right away , at first I thought it was the battery but it wasnt then i start thinking about either the starter or the crankshaft sensor my ? is how can I tell is it is the cps or the starter, the funny thing is last night as I was driving the car everything shut off in the car momentarily but the engine didnt die the rpm went down low and reved back up to normal againthis happened 3 times and this morning it took me 15 mins b4 the car would start