1992 Nissan Maxima

Engine Performance problem
1992 Nissan Maxima 4 cyl Automatic 105, 00 miles

My nissan die's when idling. But not all time, I can get in and it will drive great. And it will either start running bad sometime while im driveing or I can stop and like my boyfriend will drive and it just starts running bad. While in driveing it kinda acts like it has no power or it's not getting gas. You can watch the RPM's just go up and down real fast or it will slowly go up and down. And when I go to a stop it sometimes just die's. Like when I come up to a stop sign or a red light. I took it to one Mechanic and they said I had a blown head gasket. But my dad's mechanic said it was fuel injeter. They changed the fuel injeter 2 times now in fact I just got the car back today. My dad drove it from the shop to his house and he said that it did not mess up at all. It ran fine the whole way, But when I picked up it a couple of hours later it was doing the same thing it was doing before.