Ford Taurus SES 2002

I’m driving ford Taurus SES 2002. it will ONLY happen after driving for about 10 to 15 minutes. once the engine is at idle ( below 1000 RPM ) it will start flickering and sometime just stay on until I push the Gas pedal.

It started right after I changed my oil for the first time after bought the car (Jan 2014). so I changed the oil couple of months ago and about 1 week later it started acting like this. I brought the car to the same mechanic and they told me it’s because of the oil pump (after investigation). I called different mechanics and they say different things, like they said it might be because of bad oil filter that they installed (NOT craft). so I took the car to the lube stop and after checking the oil filter they said it was so loose and I had lost half of my oil. they fixed it and had it tight , pure some oil to the engine. I thought if the problem has been solved but after driving for about 10 minutes the problem came back. I changed the oil pressure sensor with my friends car and I still have the problem !

please someone help me figure this out.

thanks