I have a 86 samurai that will not keep a steady idle. it fluctuates at a steady pace.
I have a rebuilt 1.3 by John's foreign engines with all the go fast goodies Cams ,high compression pistons, rocker arms etc. his redline 38mm outlaw carb with manual choke, and pace header. new plugs Bosch wires and distributor cap.
this all ran fine until I did a 600 mile trip to St.Louis and back. At the end of the trip with only 50 miles to go the idle started to go up and down. almost dieing then up to 1500 and then tried to die and up down up down. I turned up the idle so it wouldn't die in traffic so the idle goes from 1000 to 2500 or so.
The problem seemed to go away and then come back mysteriously so I kept  taking it out on short trips until the problem wouldn't go away. then i started to get a high pitched squeal from what I thought was the distributor so I bought a rebuilt one. Same problem but no squeal.the old distributor looked excellent still.Looks also recently rebuilt.
checked torque on intake and exhaust. both are tight but might be too tight? I had someone else install the engine.
have a blaster coil and MSD box waiting to install but don't want to till I've figured out the surge problem.
thanks for any help or if someone knows who will work on this thing in the
Chicago land area.

not familiar with carborated setups but do they use idle air control valves? if so sometimes cleaning them can eliminate what you are describing... another thing to check would be your cat.

Fuzzy thinks you have a vacuum leak. Use a propane torch, plumbers style, outside not in garage. Start engine, open torch valve, DO NOT LIGHT IT!! Hold nozzle near all vacuum lines, intake/carb adapter gaskets etc. When it revs, you found the leak. I'm gonna bet on the carb adapter plate, they're notorious for leaking between the plates. m2c

Fuzz

I am no expert and you likely would have checked this out already, but your engine idle can surge like that if you have a cooling problem such as coolant leaking out somewhere (e.g. cracked head)... happened to me on my '95 Sidekick 16 Valve engine which is unfortunately a common problem with those engines... different engine, I know, but just thought I would add this thought to the mix...

I'll try the propane torch trick when it stops raining here.
the engine was installed less than 6 months ago. barley broken in. The radiator and water pump are new and i don't think i have a cracked head but i'll look closer.
everything is new except the coil.
new or rebuilt stuff:cooling system, engine, carb, exhaust system, (no cat by the way)