The Elegy from GTA SA with ALL tuning parts included and fully usable, along with all liveries. Fits best into IV:SA.
I've included the .max project file for anyone who wants to make their own fully tunable car.

REQUIRES v21.08.07.1 or newer of Zolika1351's Trainer/Mod Menu to work, otherwise the car is completely unusable. (Use 'Vehicle Options' - 'Pay 'n' Spray Mod Garages' to purchase the parts in-game)
PUT ELEGY.DAT INTO THE "carmods" FOLDER! (if it doesn't exist, create a folder called "carmods" in your game folder and put the .dat there)

Vehicles.ide:
elegy, elegy, car, SABREGT, BANSHEE, VEH@LOW, NULL, 100, 999, 0.2240, 0.2240, 0, 5, 1.0 ,0, livery
txdp
vehshareSA, vehshare
elegy, vehshareSA

Carcols.dat:
elegy, 0,0,49, 38,38,85, 0,97,102, 3,0,12, 6,6,4, 11,4,12, 13,13,12, 16,95,90, 24,1,12, 21,21,12, 23,23,2, 31,31,27, 32,113,34, 34,12,34, 49,13,41, 52,0,59, 62,13,69, 76,4,76, 82,85,76, 87,8,76, 89,0,4, 92,95,90, 95,95,2, 106,103,2,

Tuning part count: 16
Tuning part list:
Stock Exhaust
Alien Exhaust
X-Flow Exhaust
Stock Front Bumper
Alien Front Bumper
X-Flow Front Bumper
Stock Rear Bumper
Alien Rear Bumper
X-Flow Rear Bumper
Alien Roof Vent
X-Flow Roof Vent
Alien Spoiler
X-Flow Spoiler
Stock Side Skirts
Alien Side Skirts
X-Flow Side Skirts