If the tensioner pulley is bad, you only need to replace just that...and usually if you have one pulley bad, all three are almost bad...do them all while you can easily.
What I meant is that you can get the idler pulley bolt through the front ear of alt but not through the back ear...and thus the alt would be sitting at a slight angle. I don't know how I missed it when I did that, but it's possible. There's a bushing on the alt's ear that gets pulled out and can hang you up in trying to get it back...but you can see it going through the back ear of alt or not. Look to confirm belt is square on all pulleys.
Also, you know, guys have misrouted the belts before...nothing personal!
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