So my first question- as an extension of some other threads- Whats the best thing to use to plug unused nipples on the intake manifold? I have electrical tape and cut hose right now...

Leading to the issue- throttle response. I am missing the power I had and sometimes get back randomly. Maybe vacuum leaks opening as I accelerate. But I'm thinking about either checking the exhaust or just throwing the cheap thing out and investing in a better system (then again I will eventually get rid of this car, maybe I should go back to stock catback and just buy a good performance header?)
But it feels like when I push down on the throttle that the air is getting in there, just theres not as much power. That may be from the loss of low end torque too cuz of the bigger exhaust. It feels like theres not enough fuel to match the air coming in but at the same time my MPGs are around 22 city driving at 15mph average.

I hope this all makes sense and doesn't seem like I'm jumping all over the place...

So at the same time my timing advance reading is weird. Its now at 9.5 at idle. But should be 15. The RPMs can be 750 and the timing advance will go from 9.5 to 15. Its random. Leaks wouldnt cause this cuz then the RPMs would go up right?

So what changes the timing but not the RPMs?
And what should I do to get the air coming in to match the fuel coming out efficiently?

I know I can get all this to work- the bolt ons for more power, not a lot but enough to be proud of... Other people have which is why its annoying me >.>