My ford falcon ba 2002 is missing

My ford falcon ba 2002 is missing when idling just a little bit, it drives perfect it takes of perfect but as it idles it a little bit ruff. I put new plugs in and some injector cleaner in but it still idles just a little but ruff its just started in the last 600 kl.
does somebody know what it might be. Thanks from peter

Try using some thing like this unplug coil on plug put this between coil and plug. http://www.ebay.com/itm/282066670979/http://www.ebay.com/
Otherwise scan for codes and look for misfiring plug or injector.

Injector cleaner that is added to the fuel tank doesn't always work. The best fuel injector cleaner is the stuff that you apply directly to the injectors. Problems like what you've described are usually either fuel or fire. Clean the injectors the right way and if that doesn't work go through the ignition system thoroughly. Check the wires for continuity and test the coils. Also make sure you have the right spark plugs for your engine. If the gap on the plugs is wrong, you'd be surprised how many problems that could cause.