Knocking, Hesitation, Rought Idle And Smoke At Sart...

[Pezimistik]

I have a 96 Pontiac Firebird 3800 with 169000 miles on it, auto. When i first start the car, after its been sitting over night, it has a lil rough idle, when i press on the gas it puts really hard untill i push smoke out my exhaust, then runs fine the rest of the day. however, when i start the car, i heard a real loud knocking noise that hits for about a couple seconds then drops down to a lower knocking volume. actually, when in high rpms i dont even think you can hear the knocking noice. you cant really noticlytell untill i come to a complete stop (which knocks hard for a couple seconds then goes down to a low toned knock) or unless i rev my engine all the way. Not to mention when i start accelerating, i will press the pedal hard but the car wont pick up for a couple of seconds. like kinda has to build its way up. but when driving in high rpm, it doesnt hesitate nearly as much, sometimes not at all. Only a few times where ive actually had the car ALMOST die on me becuz of rough idle, but then picks right bak up and works just fine. I have put much thought into this n came up with the fact it could be my intake manifold....but im not sure n i want to get opinions on this...your advice is greatly appreciated