In an attempt to treat the problem, I first stopped by a local "Parts City Auto" to have the engine code(s) pulled; misfire in cylinder #4, and a "P1600", which I later learned is the Mitsubishi code for "you unplugged the battery". I replaced the plugs afterward, and they were white; a sure sign of heavy knock and a lean condition, which my A/F gauge readings supported. Thinking boost leak, I then assembled a boost leak tester from a 2" Fernco elbow coupler, a 1.5" PVC end cap, and a cheap little 5-gallon air tank from Menards, and a $0.99 tire valve stem from Pep Boys. The tester turned up an obvious leak in one of the silicone couplers holding my lower intercooler pipe, which I replaced with a piece of straight radiator tubing from NAPA; more durable, black, and a MUCH tighter fit. A followup test revealed a small leak, but I ran out of time in the day to track it down. I'll probably try a test with smoke next, to see if that makes a difference.
I've also run a bottle of Chevron Pro-Gard Fuel Injector Cleaner through, which doesn't seem to have helped; I was hoping it was simply a clogged injector. I have a new fuel filter ready to go on as soon as I get a chance, to see if that might be causing a shortage of fuel to the injectors. The next step will probably be giving the injectors a thorough cleaning to see if it's just one injector giving me grief, followed by an MCCC treatment. I've also got a 1g throttle body that I'm planning on installing, which I'm installing new o-rings in; that should eliminate any leaks from one potential trouble spot.
If, after clearing up any additional boost leaks and replacing most of the major places for crud build-up in the fuel system, the car is still not running correctly, I'll be running a compression test before I start replacing more expensive items (new injectors, etc), to make sure I'm not throwing good money away; I don't suspect there's a problem, but I want to be sure, and we need to run a compression test on Erica's 1g anyway, so we'll do both at once.
In more positive news, I managed to pick up a used-for-a-week adjustable wastegate actuator made by Forced Performance a while back, and finally got around to installing it. The stock wastegate actuator has a tendancy to blow open at higher RPMs, which means you lose boost very rapidly after about 5000 RPMs. The adjustable actuator lets you dial it in with more precision, and it comes pre-set to hold 17psi as far as the turbo can do it. Installation was a breeze; two 10mm bolts and a little clip for the arm are all that hold it in place, and the new one is a direct fit. The results were impressive: it really does what FP claims. I haven't had a chance to do a proper run with it because of misfiring, but at wide-open throttle it pulls like a banshee at 5000 RPMs now. Bottom-end spool-up seems to be affected, but the misfiring is makes it difficult to test that.