Hi, for above, when changing the drive belt tensioner, should I also change the idler pulley ? tks for advice.

 

Change it if there is something wrong with it. If it is undamaged and works fine, leave it alone.

 

The idler pulley and serpentine belt are inexpensive, so I'm going to take the opposite position and say that since its not easy gaining access to that area, take the opportunity to replace everything you can while you are there. Inspect the engine coolant pump bearing while the belt is removed - and if necessary replace that as well.

 

I can see Pat's point, but then 'while you're there', change out the water pump, timing chains, front seals, coolant lines, intake lines, vacuum lines, timing cover, oil pump, oil pump housing (is that a thing?)...
I suppose that the idler is a "why not" thing. Meh. Sure, go ahead since you're there. Can't hurt. Course, I've NEVER had an idler pulley go bad in any vehicle I've owned. Maybe you could sell the old one for a few BEFs, or Euros.

 

If the tensioner has vibrated enough to wash out the pivot axis, I'm sure the idler bearing will be noisy enough to warrant replacement. I assume the belt isn't tracking on the center of the idler and that's why you want to replace it? If that's the case I'd replace the belt as well.

 

The bearings are replaceable on the pulleys. Just pull the number off the side of the bearing (should be 6203 or something like that) and order them from vbx.com. Just be sure to get sealed bearings and not shielded. I recently did this and bearings for both idler pulleys and the tensioner on the supercharger belt were $12, shipped and were here in three days.