so for a while now my car has had what feels like a low idle miss, its very subtle so i can't really say for sure that it has to do with spark but i just did plugs cables and a cap at 100k i'm at 120k now. also (usually only when cold) when i'm accelerating on the low end of gears i hear like a rattling sort of sound, the more throttle i give it the worse it sounds it goes away between 3k and 3.5k but only while accelerating, cruising i can not hear the sound.

some more history, could be related might not be but i just did an intake manifold about 2000 miles ago, though i did hear the sound before that, it was minor, i could only hear it with the windows down going by bushes or other solid objects. it seems to be getting more noticeable, now i can hear it in the cab with the windows up. during the changing of the manifold water got into the oil. where i was i could not change the oil so as bad as i know it is i drove it 2 miles with water in the oil before i could change it. after changing it i drove about 50 miles and changed it again just to be sure but there was no water in that change (at least not enough to make a visible difference.)

anybody know what direction i should be going in? how long is a timing chain/belt supposed to last on this engine? could that cause this?

 

A rattle can be wayyy to many things to guess at. Need to pinpoint the location a bit more for help. Could be as little as an exhaust shroud, might be worse.
Rattle while sitting still, reving the engine?

 

Take a 3 foot piece of rubber hose like vacuum line size or slightly bigger and stick one side in ur ear and put a earplug in ur other ear .. Go around probing everything with the end of the hose that's not in ur ear and use it like a doctors stethoscope like to listen to ur heartbeat .. Pinpoint ur rattle very easily like this and many other noises if ever necessary again

 

I guess maybe rattle isn't the best way to explain it. i guess it could be spark knock, i've never heard it before so i'm not sure what spark knock actually sounds like but this video about engine ping seems to be exactly what i'm experiencing.
also it only happens under load/acceleration, doesn't happen at idle or with engine rev so there's no way i can do the tube in the ear method but i have used something similar to figure out that my alternator was making noise (i hoped that was what this was)

if it is in fact pinging, at 120k miles what should i be looking at first? nothing has been done to the engine it self other then the plugs, cap, wires, intake manifold, and both fuel injectors. the computer is not after market chipped (although it was at one point between 80k and 90k miles) and the plugs wires and cap were all high quality/performance. the intake was an edelbrock (don't get much choice in the way of aftermarket intakes)

 

put 91 octane in the tank and see if it goes away.
Check timing

oh and please give us some detailed info on this car you speak of.

 

I don't know why I forgot to put the actual car. It's a 91 camaro rs 305 automatic.

We don't have 91 here by default and they were out of 93 so I put 89. Didn't seem to change it. I moved the cap clockwise till it almost stalled and counter clockwise till it almost stalled and put it somewhere in the middle and though the sound was gone (or at least unnoticeable) it ran very sluggish check engine light came on and it stalled. Adjusted it clock wise engine idle picked up a little drive it same thing. Went counter clockwise a little past the previous position now the throttle responds properly but the noise is back and worse. I don't have a timing light.