Just to remind me I'm not nuts I think.

This is an ongoing issue, little under 20K miles now and I'm still stumped.

Thing is, it's subtle, to the point where it's very, very hard to try and diagnose it. The only really tangible evidence is an intermittent putt from the exhaust at idle when warmed up. This evening, for the longest time ever, it went away, idled smooth, accelerated smoother, more "free" if you will. It's done so now and then before, only does it when warmed up, not dependent on fuel level, temp, driving type, etc.
I can't isolate the idle miss to any one cylinder, pulling an injector plug or a plug wire creates a dead miss that masks the light intermittent miss, if that makes sense. Reading the plugs shows nothing odd, compression test shows my #2 a little low but close enough to the other three(and likely where my piston slap is).
I don't believe it's mechanical, I've beat on this 90 model motor for almost 20K now with no trouble.

The AMM is new, distributor plugs and wires, engine harness, LH temp sensor, all vacuum lines, injector seals, intake and all other engine gaskets before I installed it, 02 sensor, fuel filter, the pumps are quiet and show no sings of fault, have swapped the ECU, injectors, FPR, cleaned all the grounds listed in the greenbook, checked all the harness plugs, all the engine grounds, near as I can find everything works as it should. MPG is 22/26, it moves alright for a stock turbo wagon, but that damn idle miss, it has to be something.

So I ask again, suggestions? My next step is to start checking resistance on indevidual wires, at the ecu and working my way out. But all the wiring with the new engine harness looks fine, no corrosion, nothing. Willing to bet I don't find a problem there.

The only other symptom I have is timing related. I've had it at both 12 and 14 and left it at 14 btdc, I have manually checked the balancer to make sure it's not slipped also. But, when the fan temp switch on the rad kicks the elec fan on, happens in traffic sometimes in hot weather, it kicks the timing advanced to help it cool down, and the idle get's rougher under this condition.

Suggestions?