I have thrown my serp belt on my '88 4.3 about 8 times in the last 2 months I'm on my 2nd brand new belt. I keep throwing it off the idler arm. I'm thnking maybe I might need to replace the idler arm, do you guys have any ideas? Why it is doing this and what might be the fix?

 

Is the belt loose? If so, you might have a bad tensioner. If your truck doesn't have a tensioner, than you might have some belt driven accessories with loose bolts. I personally don't know if you have a tensioner or not.
That's all I can think of.

 

:not to familar with the pre 90s:

if the bearing was failing in the idler pulley it could cause the belt not to spin completelty in a circle. you would have a wobble. only other thing i could think of is what cbr said where you're not getting proper tension

 

Bad tensioner is a good bet... maybe a bent pulley?

 

Wait, I just realized the OP said Idler Arm. That's apart of your steering system, bro. You're thinking about Idler pulley. I hope.

 

yeah your right it is the idler pully I say arm out of habit and yes the belt is very tight. Could over the life of 22 years and 184,XXX miles the idler pully have worked it's way crooked a little and thats what might be causing it? I mean each time it has done it when i pop the hood there the belt is laying under the pulley next to the alternator. It makes for easy work getting back on but I sure am tired of having to fix it. Plus I dont want to get stranded someplace

 

Check the pulleys from the side while its running to verify all of the pulleys are straight. The ribs should keep it on... unless it's loose. The idler pulley should have good, strong tension if it is spring loaded, and tightened well if it is fixed.