Timing my 1989 chevy pu 350 auto?

You should see the mark jump off the scale...EFI runs very high idle timing, at least when compared to most carbed applications, but obviously only with the EST connected.

I would expect the idle RPM's to change with the difference in idle timing, however I've never really played with that specifically, since that means the engine is running off the ignition module, not ECM. Obviously when I change the idle timing through ECM tuning even a 2* difference is noticeable idle quality.

The truck should be turned off, wire disconnected, started, base timing set, shut off, wire re-connected, started, ECM cleared only if showing a trouble code. BTW pulling the ECM fuse is the smart/easy way to clear the ECM without losing your presets/clock, and it takes mere seconds to clear. About as long as it takes to pull/reinsert the fuse.

Try timing as I mention, see if that fixes it. Surging idle could be a bunch of things, if that doesn't fix it, check with your local library (if decent size metro area) and find out if they can get you the factory GM wiring/service manuals for your truck. If you are asking if the ECM is the cause of an idle surge, you need to get the manual. Replacing parts on a hunch just means you haven't tested enough. :)

You did set base timing to what the sticker says, right? A couple of degrees either way won't kill you, but too much one way or the other can cause problems.

Is check engine light on? If yes trouble codes need to be cleared on ecm. On some gm products can disconnect neg bat terminal for a few secs and may fix problem. On computer controlled engines you can't run around disconnecting random wires, get you in trouble every time.