A new set timing gears and chain fixed my hesitation problem, but I still have problems keeping the idle steady. This only happens off and on and usually when it is cold and wet outside. When the engine warms up, the idle drops to around 550-600 in drive (where I like it), but at times it just keeps dropping. Once it falls below 250 the engine will stall. The engine will start back up, but usually the idle only comes back to normal after it is turned off and sits for awhile. If I put the car in park, the engine does not speed up, but will die just like in drive when I am having this problem. Another problem (related???) is when I go into a store for 5 minutes and and then start the bronco back up, it will start at 1500 and rev up to 2000 RPMs in Park and will not drop down. When I put it into drive, it drops down to 1000, and will stay that way for 5-10 minutes even if the engine is blazing hot. I backed off on the choke and it did nothing to help the problem. The idle is set to cold Park1200,Drive900, hot Park700, Drive550 when working and I used the dashpot as a stop for the hot drive setting.
Specs:
85 bronco 351 HO, 4X4 c6 tranny
original Holley 4 barrel carb (rebuilt a year ago, but I don't know how well)
original Duraspark II system (could it be losing spark off and on?)
no vac leaks that I know of
new plugs, wires, cap, rotor
compression check 130 all cylinders
11 mpg (don't know if it is relevant)

This is the last problem that I have and once I get this fixed, I'll be in good shape. What should I start replacing? Thanks for any ideas,
Dan

 

I just tested it some more. I noticed if I create a major vac leak unhooking a large hose that comes off the back of the engine the idle jumps back up. It is starting to drop idle more often now even when it is not wet outside or very cold.
Could this have something to do with the vac advance? where is the vac advance and how do I test/ adjust it?
Thanks, Dan

 

It sounds like a vacume leak to me
when you have it idling does the engine stumble and visibly rock back and forth? I'd run to the store and get a vacume gauge, like $5-$10 and its very usefull to diagnose problems, usually they have a color coded gauge of red/green and have a mark for "normal" vacume, helped me find out that I hadn't resealed my lower intake correctly after I ported/polished my intakes, heh whoops

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