Whats up people this is my first post on here so 2 and a half years ago i bought a 99 Galant GTZ 3.0 for $2000 usd 112,000 miles mint from a friend tuned with intake and exhaust i have put alot of work into the car just up keep like o2 sensors brakes rotors fixed the exhaust from the headers back and much more. My question this year of car worth tuning? and what are a couple of things to increase my horse power the most? Last question when i turn my whip on cold start my rpms go high then low reving high and low for about 2 mins then stops any ideas?

thanks for your imput.