When I am driving and I let of the gas say at 50 mph the rpm is at around 1500 than if I let off the gas the rpm tach will randomly drop to 1000 than back up to 1500. Is this normal ? When I let off the gas I am just coasting down hill so the speed stays the same but the rpm will go up and down between 1500 and 1000

 

Mine doesn't do that pecker, don't know if it's normal though.

 

Check your compression in your cylinders. Sometimes bad compression can cause that. Then if you can check the timing chain to see if that's not stretched.