sr20det noise

[drft911]

my sr started to make a noise coming form the front of the engine, its kind of in back of the water pump and when i first heard it i thought it was the the water pump so i replaced it, but now im pretty sure its the timing chain or guides. the noise sounds like a ball bearing thats going bad.Has any one had that problem? Another problem is the idle, it has sometimes a stable idle of 1100-1200RPM then when i rev and it kind of sounds like it wants to shut off, and it has when i get off the freeway. then sometimes it jerks when im driving but its very mininal.IACV? thanks