My orange '76 242 is running poorly. Could someone give me some advice?

Problem with 1976 242DL w/CIS (K-Jetronic):
Loping, inconsistent idle. Sometimes it runs high RPMs, sometimes low, sometimes stalls, all depending on weather, humidity, rain, sun. Because of this, I am constantly adjusting the idle speed knob to find the proper idle speed. Often I must re-adjust when engine warms.

I know that the cold start injector, thermo-time switch, and auxiliary air valve are functional. The aux air valve is sort of broken in such a way that I can rotate it to control the amount of air entering the engine when cold.

I have replaced the fuel injector seals. When warm (and cold) the engine exhaust smells of gasoline, and often is slightly white even on a warm day (too rich?). The timing is 15 deg BTDC with the vacuum retarder on the distributor unplugged and capped. I have removed the air pump, and disconnected the EGR and any peripheral vacuum lines for the emission system in order to make troubleshooting easier.

The compression is 150 across the board. The vacuum is a consistently meandering 13-15 inches, and the needle on the gauge states the ignition timing is too late, but like I said, it's a confirmed 15 deg BTDC.

The ground strap on the valve cover is filthy and covered in grime but intact, and I recently took the rubber boot off of the air mass meter venturi and cleaned the boot and the little metal disc.

I haven't troubleshooted the fuel pressure regulator, and don't quite know how, I'm a bit of a newbie with this. I thought it might be the regulator, but I'd like to know other people's opinions.