Toyota Repair: Rough idle 1999 Avalon XLS, vacuum leaks, last computer

Question
I experienced a rough idle followed a day later by a check engine light.  The mechanic at a local garage said the computer showed a problem with the number 1, 3 5 cylinders.  First (after testing for vacuum leaks) they changed the ignition wires; the problem persisted, so they changed the coils.  The problem has not gone away.  A Toyota bulletin says the injectors should be changed, but another mechanic whom I used for years said he has never had to change the injectors  on a Toyota.  Also, why would only 1, 3, and 5 go bad.  Actually, the last computer check showed a problem now only with 1 and 3.  Would a pressurized injector cleaning be useful?  What else could be wrong, other than the injectors themselves.  Thank you.

Answer
Rowan,

#1, 3, & 5 are all on the same side of the engine so I would look for something in common to all those cylinders. First I would check your timing belt. If it jumps a tooth on one cam it would throw all 3 cylinders off.  I agree with your first mechanic that Toyota injectors hardly ever go bad.  It does help to clean them once in a while, but I don't think that is your problem here.  Check that T-belt and let me know what they find.