Correction by Piiap

public OnPlayerKeyStateChange(playerid, newkeys, oldkeys)
{
    if(IsPlayerInAnyVehicle(playerid) && GetPlayerState(playerid) == PLAYER_STATE_DRIVER)
    {
        if(newkeys == KEY_CROUCH) // FLIP
        {
            if(EnableBoast[playerid] == 0)
            {
                new Float:PX, Float:PY, Float:PZ, Float:PA;
                GetPlayerPos(playerid, PX, PY, PZ);
                GetVehicleZAngle(GetPlayerVehicleID(playerid), PA);
                SetVehiclePos(GetPlayerVehicleID(playerid), PX, PY, PZ+1);
                SetVehicleZAngle(GetPlayerVehicleID(playerid), PA);
                PlayerPlaySound(playerid, 1133, 0.0, 0.0, 0.0);
            }
        }
    }
    if(IsPlayerInAnyVehicle(playerid) && GetPlayerState(playerid) == PLAYER_STATE_DRIVER)
    {
        if(newkeys & KEY_SUBMISSION)
        {
            if(EnableBoast[playerid] == 0)
            {
                new Float:vx,Float:vy,Float:vz;
                GetVehicleVelocity(GetPlayerVehicleID(playerid),vx,vy,vz);
                SetVehicleVelocity(GetPlayerVehicleID(playerid), vx * 1.8, vy *1.8, vz * 1.8);
            }
        }
    }
    if(IsPlayerInAnyVehicle(playerid) && GetPlayerState(playerid) == PLAYER_STATE_DRIVER)
    {
        if(newkeys & KEY_YES)
        {
            if(EnableBoast[playerid] == 0)
            {
                new Float:x, Float:y, Float:z;
                GetVehicleVelocity(GetPlayerVehicleID(playerid),x,y,z);
                SetVehicleVelocity(GetPlayerVehicleID(playerid),x,y,z+0.3);
            }
        }
    }
    return 1;
}