My 305 IROC has recently started giving me some problems. The engine note has changed drastically, there is a slight hissing sound when accelerating, a gauge mounted to my intake (possibly to the fuel rail, but im not sure) is going completely nuts, fluctuating from 0-65 psi completely at random, and when last I gave it heavy throttle, there was profuse smoke from the side of the engine- a leak of some sort hitting the header (I could hear the sound of something hitting it then evaporating). Now, I have been told I could have an intake manifold leak or a head gasket leak. I dont think it would be a head gasket problem, because I have been told that if the car sits overnight on a level surface and you check the oil level in the morning, coolant would be noticeable on the dipstick if the head gasket was leaking. HELP ME!!! What do I do? I like my 'roc too much to have it not moving (well, it moves, just not as fast)

 

Poor performance, hissing through the exhaust, really sounds like the exhaust is restricted.

Plugged cat, smashed pipe, etc...