99 a8 no tach hard start
 

First post long time reader.had my share of newer a4s but recently picked up a 99 a8 quattro 4.2.car has 145k on it.all service records.checked the car out.used the vag .no codes.car ran perfect.had it for two days tach started bouncing around,car died.would restart but had to crank for 5-10 seconds.pulled a cam positon sensor.checked the wires replaced the sensor.then it pulled a cam position and crank position sensor.checked wires and changed the crank sensor.car will fire up but so etimes have to crank longer than normal.tach is still dead .car runs and drives fine.im stumped.im leaning towards and electrical problem.thanks in advance for any help on whats next.