[glatt]

It is fuel injected.

So in addition to hooking it up to a code reader, the shop manual says to:
- check oxygen sensor
- check throttle position sensor
- check engine coolant temperature sensor
- check MAP sensor
- check if problem occurs when engine is running Rich or Lean (I think it's lean when it's hot, which it is)
- check evaporative emission (EVAP) control system
- check fuel injectors
- check fuel pressure
- check ignition voltage output
- check spark plugs
- check spark plug cables
- check ignition timing
- check for vacuum leaks
- check the ECM/PCM grounds
- check ECM/PCM for A/C signal
- check EGR
- check battery cables
- check A/C refrigerant pressure
- check PCV valve
- check for broken engine mounts
- check valve timing
- check low compression
- check bent push rods
- check worn rocker arms
- check valve springs
- check camshaft lobes

Holy crap. I can rule out about half this stuff, because it doesn't make the metal clanking sound of worn valves or bent push rods or anything like that. And it has nothing to do with the A/C being turned on. And we just replaced the PCV valve. The spark plugs and distributor cap are not as new as I thought they were (they are about 30K miles old,) but the cables look good and clean on the outside.