It has a knocking noise under the hood when I first start up in the morning. I had the injectors replace when they were recalled in 1997. Could the lifters being going or what could it be. Does anyone know why when I first start out in the morning going down the road with a bucking between gears before the car reaches the warm up period? Also, when the a/c is on I don't get the much air flow it is on high. I know that it is suppose to gradually increase speed and which mine does not. After the 1/4 mark on my 1984 300zx nt air switch slides to increase air flow and it stays the same speed from the 1/4 mark to high and why?