Random multiple misfire at idle

Well its been a while since I've been on the forum, so long in fact that I forgot my login. Now I have a new one but its still the same old aveosam. Anyway a while back I had my head gasket fail and oil caused havoc to the spark plugs and ignition system. We replaced all of the plugs, wires and coil pack, but the aveo still runs real rough at idle and if you let it sit at idle, the check engine light registers random multiple misfires. As soon as you give it some gas the misfires go away. We thought it could be related to a vacuum leak because they brakes have also started acting weird right after start up. I've been driving my aveo since 2004 and I notice ever little difference. Essentially it feels like the engine is over powering the brakes initially but after a few miles it goes back to normal. I was wondering if anyone else has ever experienced random multiple misfires in their aveo. We checked for vacuum leaks but found none. It's weird that it runs like crap at or around idle but I get 35 mpg still.

I am in the process of return my intake back to stock to see if that has any affect. Right now I have metal pipe from my tb to the intake box. I opened up the box into the wheel well and smoothed out the inside above and below the filter (K&N filter). The setup is really stiff and the engine moved quite a bit and pulls on it.

If you got any ideas what it might be let me know. Also if you have any leads on where i can find a stock 04ish intake box and intake flexible pipe let me know.

have you solved the problem yet?

No it must b leak we can't find

a lot of older threads popping up that i never saw..

i am not sure if the 04 needs an idle learn procedure because its cable throttle, but you could try it?

have you tried cleaning the throttle body? if the butterfly cannot close, then it will be sucking too much air for the fuel. however if this was the issue you would/should have a tps code.

the random misfire code is p0300 only?