Are you sure that the alternator's OK? The voltage regulator may be fine and it may be charging the battery normally. However if one or more of the diodes has burnt out, a small AC voltage may be leaking out.
An AC ripple test will determine if the alternator is at fault.
Yes i changed it same thing i decided to take to dealer and they told me it could been something in the timing or the computer but i doubt its the timing the car runs good
You could have worn cam phasers which is common on high mileage engines (and on lower mileage engines that have been driven hard). The symptoms are often intermittent, especially in the early stages.
Do you hear any ticking noise from the front of the engine at idle (not the normal clicking of the injectors)?
Another possibility is that the mesh screen inside the VCT solenoid oil control valves is clogged up. This is common on engines where oil changes have either been neglected or poor quality oil used.