[EiresJason]

What about this?

pawn Код:

CMD:engine(playerid, params[])
{
    new playerstate = GetPlayerState(playerid);
    if(playerstate == PLAYER_STATE_DRIVER)
    {
        new vehicleid = GetPlayerVehicleID(playerid);
        new engine, lights, alarm, doors, bonnet, boot, objective;
        GetVehicleParamsEx(vehicleid, engine, lights, alarm, doors, bonnet, boot, objective);

        if(engine == 1)
        {
            engine = 0;
            SetVehicleParamsEx(vehicleid, 0, 0, alarm, doors, bonnet, boot, 0);
            SendClientMessage(playerid,-1,"The vehicles engine has turned off!");
            return 1;
        }
        else
        {
            engine = 1;
            SetVehicleParamsEx(vehicleid, 1, 1, alarm, doors, bonnet, boot, 0);
            SendClientMessage(playerid,-1,"The vehicles engine has turned off!");
        }
    }
    return 1;
}