[Shinja]

PHP код:

CMD:engine(playerid, params[])
{
    new vehicleid, carid, model;
    if(!IsPlayerInAnyVehicle(playerid)) return SendErrorMessage(playerid, "You are not in any vehicle.");
    if(!IsEngineVehicle(vehicleid)) return SendErrorMessage(playerid, "This vehicle doesn't have an engine.");
    if(GetPlayerState(playerid) != PLAYER_STATE_DRIVER) return SendErrorMessage(playerid, "You can't do this as you're not the driver.");
    if(PlayerData[playerid][pInjured]) return SendErrorMessage(playerid, "You can't do this while being injured or dead.");
    if(ReturnVehicleHealth(vehicleid) <= 300) return SendErrorMessage(playerid, "This vehicle is totalled and can't be started.");
    if(CoreVehicles[vehicleid][vehFuel] < 1) return SendErrorMessage(playerid, "The fuel tank is empty.");
    if(carid != -1 && Car_IsOwner(playerid, carid) || CoreVehicles[vehicleid][vehTemporary] || CoreVehicles[vehicleid][vehRental]  && PlayerData[playerid][pRentedVehicle] == vehicleid || CoreVehicles[vehicleid][vehJob] || (PlayerData[playerid][pFaction] != -1 && CarData[carid][carFaction] == GetFactionType(playerid)) || PlayerData[playerid][pCarKeys] == carid)
    {
        switch (GetEngineStatus(vehicleid))
        {
            case false:
            {
                SetEngineStatus(vehicleid, true);
                ShowPlayerFooter(playerid, "You have ~g~started~w~ the engine!");
                SendNearbyMessage(playerid, 30.0, COLOR_PURPLE, "** %s inserts the key into the ignition and starts the engine of the %s.", ReturnName(playerid, 0), ReturnVehicleModelName(model));
            }
            case true:
            {
                SetEngineStatus(vehicleid, false);
                ShowPlayerFooter(playerid, "You have ~r~stopped~w~ the engine!");
                SendNearbyMessage(playerid, 30.0, COLOR_PURPLE, "** %s inserts the key into the ignition and stops the engine of the %s.", ReturnName(playerid, 0), ReturnVehicleModelName(model));
            }
        }
    }
    SendErrorMessage(playerid, "You don't have the keys to this vehicle.");
    return 1;
} 


Show us the used stocks like IsVehicleEngine...ect
Are you putting the code inside OnPlayerCommandText brackets? if you have some lines there show us