So far my mods are:

CAI
Header (4-2-1)
Highflow Cat
2.5" pipe to muffler (straight through kind)
10mm wires
Ground system

What its doing now is idling very weird and hesitating under heavy acceleration, its ok for like 6 seconds and then like chokes and gets really rough for a bit when it idles. I just got my exhaust done from the cat back. The whole day after gettin the exhaust done it seemed fine, then the car sat for about 4days after which I put on my 10mm wires which it sat for another 2 days. Today i decided to take it for a spin with the new wires on. At first it seemed ok until i got it warmed up. It kept wanting to die. Another thing is that going at half throtle i got great power but when i floored it, it just slowed and seemed like it was either gettin too much gas or something like that. it also sounded like it was backfiring constantly inside the muffler (like rumbling weird).

 

when you hit gas at idle, and then take foot off it does it go down to a low RPM, then come back to a more normal idle?

If so its vacuum o.o

 

hmm, where could I have messed up my vacum? I dont think i pulled or removed any lines. But it does drop low rpms after reving then go back to normal.....kinda normal anyway

 

Im not getting any CEL. I just unplugged my battery for 20min then turned it on to let it idle....its still idling crazy...it is fine for like 3 seconds then gets pretty rough for about 5 seconds and repeats.

the engine is a d16z6 if that helps. Only mod I did before I noticed this was sparkplug wires (10mm) could that be the problem?

 

make sure ur wires are securely plugged into your distributor.. happened to me once, one wire was loose.. i was running on 3cyl :doh:

 

i figured it out, since I no longer have my stock wires I had to do some swapin with my 4dr (damn i love havin swapable parts). I put all wires from my stock 4dr on and started putting the new wires on 1 at a time and started the car after each swap. #1, idled fine and no probs, #2 idled fine no probs, #3 idled fine with no prob, #4 wire, problem came back, I tripple checked the connection and it seemed fine. Guess in the end it was just a defective #4 wire. Time to get hold of the seller....Oh and I didnt go cheap on these wires so now Im mad that I spent alot and still got crap.

 

Is it still backfiring?

 

I know you figured out your problem , but for further reference a vacuum leak CAN just occur out of the blue, usually from cracking vacuum lines.