Sounds like the hall sensor is going bad. Spray some electronic coolant spray on the sensor next timethe car stalls. If it regains running properly, go with?? changing the sensor out. Another problem I have found on a few stal depairs is the fuel pump relay gets an intermediate
connections. Check all you related grounding points

Two suggestions -

1 - Look in the 700/900 FAQ - your car shares a lot with those models.

2 - Take it to a dealer - I have never had to pay for more than one part when any of our 9 Volvo drivers had an issue. Last year my dealer had a special - 1 hour's troubleshooting for free with a written report.

We have done all the suggested steps;

Crank position sensor replaced
Throttle body cleaned
Trans fluid was/is fine,
Ignition amplifier was replaced,
Fuel pumps appear to be fine.

The two things that make this tough are:

1) we can't figure out if its ignition or fuel. We're really starting to wonder if it is an electrical issue

2) It ONLY happens at first start after sitting in the morning when I leave for work. After about 15 minutes of running, the problem goes away and will not reappear until the next morning. Also, it is humidity based. We live in Michigan where it tends to be a bit moist in the morning. My car will sit for 8-10 hours while at work and start up just fine. This ONLY happens in the morning. It is getting worse. Now, the car stalls for at least ten minutes and will often non want to restart. It pops and shakes and does have a fuel smell.

Any other suggestions on where to go? We've pretty much replaced all the parts, cleaned, checked and rechecked and nothing has helped.

What about the fuel pump? They don't last forever and they don't fail all at once.

Reseat the connector on the ignition power amplifier stage in front of the battery.

If that makes no difference, replace the crank position sensor.

--
Art Benstein near Baltimore

Have an awesome day and know that someone has thought about you today...I did.

So I am assuming this is an automatic transmission?

"Looked for possible vacuum leaks, like hoses and PCV system"

With your eyes or with an unlit propane torch, WD40 or similar sprayed on all the connections?

I did not see cleaning the throttle body mentioned (but I might have missed it) the second that throttle switch opens, the air all comes through the throttle body and a badly gummed up one will have challenges with the transition.

Finally, check your transmission fluid (if an automatic). If low, the pump can cavitate at stops, suddenly run in clean fluid, attempt to jerk forward and cavitate again...this rarely causes a full stalling of the motor but it can.

1991 does not have the under hood 20 amp blade fuse, correct?

Additional things:

Looked for possible vacuum leaks, like hoses and PCV system.
Fuel injectors are only a few years old and they are new Bosch ones. So if this was the issue it would run bad most of the time.
Cleaned connections on connectors, and Fuel ECM, and ignition ECM contacts
Replaced fuel pump relay.
Checked fuse # 4 that goes through the fuel injection relay that turns on ignition system
Replaced spark plug wires, and coil wire
Inspected cap and rotor
Replaced ignition coil
Replaced MAF sensor with a used Bosch one.
Checked Throttle switch adjustment.
Checked fuel pressure 36 psi with vacuum, 46 psi with out vacuum connected.
Checked all connections.
Removed battery ground cable checked for resistance, cleaned both ends and used electrical biting style washer on block.
Did a compression test several months ago was 155 highest , 145 lowest. If I remember right , I have it written down, I know it was not lower than 145 for sure.
No signs of exhaust leaks.
Used CRC connector cleaner than followed up with Pro gold 5.