[FireFox_]

pawn Код:

forward CarHop(playerid); // On Top of your script

pawn Код:

public OnPlayerCommandText(playerid, cmdtext[])
{
    if(strcmp(cmdtext, "/carhop", true) == 0)
    {
        if(IsPlayerInAnyVehicle(playerid))
        {
            SetVehicleVelocity(GetPlayerVehicleID(playerid), 0, 0, 5.0);
            SetTimer("CarHop", 5000, 1);
            return 1;
        }
    }
    else
    {
        SendClientMessage(playerid, 0xFFFFF, "You are not in a vehicle");
        return 1;
    }
    return 0;
}

pawn Код:

public CarHop(playerid) // Put somewhere in your script
{
    SetVehicleVelocity(GetPlayerVehicleID(playerid), 0, 0, 5.0);
    return 1;
}

Script not tested