Well, as the Lex has now hit the 6 year mark with 48k on the clock, I thought it was time to change the timing belt. As I'm 22 and a poor student 
, I don't have the freely available cash to pay a garage to do it so I thought I'd have a go myself and I thought how hard can it actually be and I found that...............well, it's not that difficult actually! I was pretty nervous before I started, but when I got stuck in, it was no problem for a DIYer.
I had it completed in a few hours and I have no real mechanical experience, the most I have ever done is replacing shocks, springs and the basic bits and bobs like oil and filter changes.
I haven't seen any guides on the forum so I thought I'd take a few pictures along the way to show you guys, so please see below...........
For the record, I used genuine Toyota Parts which consisted of the idler, tensioner and timing belt. My other belts seemed perfectly fine so I didn't bother replacing them
First, take off the air box and air duct then remove the coils and spark plugs
Then, take off the bottom engine cover and drain the coolant, detach the pipes/electrical connectors and remove the radiator/fans
Remove the power steering, air conditioning and alternator belts
Loosen the crankshaft pully bolt and line the yellow timing mark up with the '0' mark on the bottom timing belt cover as shown below (make sure the car is out of gear)
Remove the top timing belt cover and make sure the dot mark on the camshaft pulley is lined up with the timing mark at 12 o'clock. If it isn't, turn the crankshaft clockwise 360 and it should line up perfectly (sorry, forgot to take a pic of this!) FROM THIS POINT ON, IT IS VERY IMPORTANT NOT TO ROTATE THE CRANKSHAFT OR CAMSHAFT!
Now the crankshaft bolt is slackened and the camshaft and crankshaft are lined up with their timing marks, remove the crankshaft pulley. Officially you need the special tool, but improvise, as you an see, I used a few little taps of a lump hammer (very gently of course) around the whole outside of the pulley to gently loosen it and then pulled it off
Remove the waterpump pulley by undoing the four bolts to allow you to gain access to one of the bolts holding the bottom timing belt cover on. Then, as if you hadn't have guessed.........remove the bottom timing belt cover
As you can see in the pic below, my timing belt was frayed and had a few chunks out of it, but was not too bad.
OK, now undo the idler bolt and remove the idler. Then, remove the timing belt.....there we have it! it's off!
Then remove the tensioner using some allen keys and fit the new one in it's place
Fit your new timing belt, starting from the crankshaft timing pulley (keep the belt nice and tight) going clockwise, around the new tensioner, around the camshaft timing pulley and back down to the crankshaft timing pulley. Fit your new idler to keep the belt tight and that's it! The new timing belt is on!
It's a good idea to rotate the crankshaft pulley clockwise at this point, just to check that the timing marks still line up after the engine has been turned.
Then, it's just a simple case of refitting (or replacing) the other belts, pulleys, radiator/fans (don't forget the coolant!), spark plugs, coils and air box which have already been taken off, and it's time for a cup of tea!
All of the above I performed with a good socket set, spanners, some allen keys and a hammer. According to the manufacturer's guide, some special tools are required, but to be honest it just requires a bit of something upstairs to improvise. At the end of the day, no garage are going to stock every manufacturers special tools to do a job on a car which they may only see once or twice a year, they always improvise!
I'm no expert and I didn't run into any problems at all, there's plenty of room to work under the bonnet of the IS. All you really need to remember is not to let the camshaft or crankshaft move out of position when the timing marks are aligned and do not rush the job.
Easy peezy! Hope this helps someone
Kev
