Are you running Linux with Gnome-Shell, installed packages and auto-suspend is broken? You can use this bash script to force suspend when system is idle!

autosuspend.sh

#!/bin/bash

log()
{
    echo "$(date): $@" >> /tmp/autosuspend.log
}

load_threshold()
{
    DOTCONFIG="$HOME/.autosuspend"
    if [ ! -e "$DOTCONFIG" ] ; then
        echo "auto-creating $DOTCONFIG"
        echo 5 > "$DOTCONFIG"
    fi
    IDLE_THRESHOLD_MIN=`cat $DOTCONFIG`
    THRESHOLD_MS=$((IDLE_THRESHOLD_MIN * 60 * 1000))
    log "suspend idle time threshold:\
$THRESHOLD_MS ms ($IDLE_THRESHOLD_MIN min)"
}
init()
{
    IDLE_THRESHOLD_MIN=$1
    INTERVAL_SEC=$2
    [ -n "$INTERVAL_SEC" ] || INTERVAL_SEC=10
    load_threshold
}
suspend_when_idle()
{
    MAX_DIM_TIME_MS=$((1000 * 30))
    while true ; do
        sleep $INTERVAL_SEC
        IDLE_TIME_MS=$((`xprintidle`+ 80))
        if ((IDLE_TIME_MS > THRESHOLD_MS)) ; then
            log "idle time: $IDLE_TIME_MS, suspending"
            gnome-screensaver-command --lock
            sudo pm-suspend
        fi
    done
}
monitor_threashold_change()
{
    while true ; do
        inotifywait $DOTCONFIG
        load_threshold
    done
}

init
monitor_threashold_change &
suspend_when_idle

Notes:

1. Works on gnome-shell (only)
2. Install dependencies (ubuntu-gnome 14.04):
   apt-get install xprintidle pm-utils
3. sudo pm-suspend needs to run posswordless. One way is to create /etc/sudoers.d/power as below and add your user to the powerdev group

$ sudo cat sudoers.d/power
%powerdev ALL=NOPASSWD: /usr/sbin/pm-suspend,
/usr/sbin/pm-suspend-hybrid,
/usr/sbin/pm-hibernate