i have a 1999 f150 lariat, i was under the hood today checking things out and i noticed that when i open the throttle there is a large hiss, or suction (cant really tell, just know its air) coming from the top of the motor. the noise comes just as you crack the throttle but before the motor revs. it is also in synch with the throttle, if i push the throttle wide open real fast its sounds like a high pressure noise, were as if i just crack it a touch the noise is more faint. also, i do not know if this is related but i also hear a ticking coming from the top of the motor. around the plugs, injectors, intake.. somewere in there. a very light sounding tick cut steady with the idle... anyone have any ideas?

 

If you have a propane torch don't lite it just turn it on low and hold it by the noise area, the motor will pick up in RPM whenyou find the leak area. It is vacuum. It can be a hole in a vacuum hose, a hose off, a loose throttle body/gasket, or even a crack on the intake plastic tube. Good luck. Also carb cleaner spray will work. Depends on which you have. Good hunting!

 

The air sound is normal intake noise.
As far as the noise. Injectors make a ticking sound.
Everything sounds normal here. But to be safe, check your plugs. They should be torqued to 28 ft/lbs

 

I agree with Toyz. If you have no codes and the truck is running fine then its normal. Injector tick is normal as well.