Car stalling AGAIN, Updates- none of them good. Options

[rjames]

Drove around for 30 minutes in 80+ degree weather. All arterial roads, so several stop lights, etc. No problems until I was almost home. Car stalled when I stopped at a light. RPMs just dropped to zero. Was able to start it again with a little difficulty and had to keep my foot on the gas to keep it from stalling out again. Power seemed ok though the rest of the way home (I think). It stalled once again at a stop light a couple of blocks from home and then again when I pulled in the driveway. I let it sit for 30 seconds, started it again and it idled just fine. Rock solid at 1000 RPMs. Pulled it into the garage where it sits now.

Prior to today the car has been running and idling perfectly since I went through the FI parts last year, which included installing a 123 distributor, new CHT sensor, a newly rebuilt mps (calibrated for correct afr on my engine), new vacuum hoses, NOS throttle body, rebuilt injectors, new fuel pump, valve adjustment and timing.

I haven’t checked the AFR since last year, not sure why it would change though.
It’s a ‘75 so the fuel pump is in the front, so I can rule out vapor lock I think.

Anyone have ideas as to why it would be stalling?

[rjames]

Update to the ongoing saga..apologies in advance for the long post.

Installed a brand new ignition harness (a work of art by Jeff B) but the stalling issue remains, although it took a bit of a different shape yesterday.

After installing the ignition harness, I drove the car without any issues for ~30 minutes trying to get the AFR dialed in on the MPS. Drive, pull over, adjust, repeat. Idle always steady at 1k. When I pull over to make another adjustment, before touching anything the idle starts dipping to almost stalling the car and back up to 1k over and over as if the MPS diaphragm had just cracked. After about a minute of this as I'm wiggling wires, checking hoses, etc. While it's doing this the AFR is super lean (~16+), yet the only way I can keep it running for the drive home is to open up the throttle body screw to let more air in and stay on the go pedal. I'm only 4 miles from home, but the AFR is so high that I worry about cooking the engine so I pull over after 2 miles to let the car cool off a bit. I get impatient and after several minutes start it up again and within a few minutes of limping home the problem goes away and the car is back to normal, but when I get back in my driveway the problem returns and I can't keep the car running. I check the MPS and it's holding vacuum just fine.
Something that I noticed as it was surging was air coming out of the hole in the passenger side tin that is to the left of the distributor. At first I though a hose had come disconnected. Can't remember if I feel that air blowing when the car is running normally and since it's not running at the moment, I can't check. Maybe this is just the from the impeller?
So do I try replacing the injection harness now?

And a side question about MPS adjustment and cold idle:
I was able to get the AFR to ~ 13.4 for par load and 13 for WOT. Maybe not ideal, but the car seems to like the AFR on the rich side. However, the AFR at idle is only ~12.5-12.9. If I try to raise it by adjusting the MPS, the part load AFR is then too high. If I try adjusting it using the throttle body screw and ECU knob, the idle is too high.
In other posts I see where people have an AFR above 14 at idle. (IMG:style_emoticons/default/confused24.gif)

Lastly, I have a working AAR valve, but when the car is cold the idle speed only goes up to ~1100 rpms or so. If I plug the hose the car dies, so I guess it's doing it's thing, but my understanding is that I should be seeing much higher RPMs when cold, no?