Hi, another problem with my Waja. Need some help here.

A few symptoms :
1. On idle(immediately after start engine), RPM like fluctuate and feels like the engine is going to stall in any time, have to rev the engine to make sure the engine's alive.
2. While driving, if on high speed/RPM, it's still ok(just some sound from the engine area I think, sounds like metal/gear knocking), but if the driver breaks or slows down the car, it feels like the car will stall(in fact, it stalled a few hours ago in the middle of the road). When the driver slows down the car, the battery indicator light will turn on, but it will turn back off if the driver press hard on the pedal.

What may be the cause of the problem?Someone said that the car needs to be overhauled, is it?

not good after reflash?? aiyoo..
so how to improve pickup or torque then?
i'm not a top speed guy.. i feel wasted my car can go 200kmh when the fastest i go is only 160kmh..
so how to convert those top speed power to increase low rev torque?

i'm using 4-2-1 header.. stock piping with s-flow muffler.. catcon removed..
engine wise basic mods only like UTR ultramesh air filter and pro rallye plug cables.. didnt change to iridium plugs as steven said it was not advisable.. then got reflashed by steven, on the road tuning..

my waja was great after reflash up till dec 2010 when i upgraded from stock oem rims to 16" taiwan..
now i feel alot of torque is gone.. change back to 15" rims and problem solved?

should i get K&N air filter? or open pod setup?