Billy,
Ok as posted do the filters - you would be amazed at what they can do for you.
Everyone is right on with the additive, a good overdose does wonders for these mechanically injected fuel lubed injection pumps and injectors.
Now the sputters a bit when returning the idle says to me that the meter valve in the injection pump is complaining a bit - the over dose of additive should free that up a bit. It won't fix it but will make it last a ton of miles. key is keep using the additive with these IDI's they (fuel system) are lubed by the fuel.
Also check for wettness around the injector line caps, they are famous for leaking. If leaking there are 2 orings under each cap that will need to be replaced. Problem is the caps are made out of plastic and stretch over time so they should be replaced as well. Upside is they come as a kit from your local injection pump/diesel shop typically made by DIPACO. Here is some information I put together on this.
The pump and inj kit contains these items.
Spring clips/hose clamps
16 injector orings
8 copper washers
8 return line caps (4 straights - 4 right angle end/corner caps
6 feet of return line hose
The above is the normal return line kit contents but this kit also has
1 oring for injection pump inlet
1 large oring for injection pump to gear housing shaft seal
2 rubber seals for fuel filter head hard metal lines
1 rubber seal for injector pump hard metal line
3 new injection pump to gear bolts.
Kit part number is
DIPACO DPE73100 Pump and INJ Kit $40.68 plus tax at local diesel shop.
Now I listed the complete contents of each kit, you will notice there are rubber seals on the hard metal lines leading to and from filter head, these should not be overlooked as sources for air leaks as well.
Let us know how it goes...