I'm trying to troubleshoot an intermittent stalling issue on a '94 940 wagon with Bendix/Rex/Regina fuel injection and ignition system.

Symptoms: While the car is at speed (and occasionally at idle), it will stall and gives the impression of a temporary ignition cut-out. It is very infrequent and it has never happened to me while test driving it, but the owner is now experiencing it several times a week. Sometimes the interupt is as brief as a 1/4 second and the engine resumes power & operation without requiring a restart. Sometimes it completely stalls and requires a restart. Twice now it has stalled and failed to restart (until I showed up), but does not otherwise exhibit symptoms characteristic to a heat-soak/hot-restart issue. The owner says that the Tach bottoms out rapidly when the problem occurs, which would point to an ignition system issue. The stalling is immediate and the engine does not sputter. -it's either running fine or drops dead.

Relavent Service:
-RPM Sensor in bellhousing was replaced about 6 to 9 months ago.
-RSR (radio supression relay) was resoldered and resealed a month ago and symptoms did not improve.
-RSR was replaced last week and symptoms have not improved.
-other relavent maintenance needs are kept up and car is well maintained (fuel filter in the last year, new main fuel pump 1 year ago, synthetic oil, etc, etc).
-most ground connections have been cleaned in the last month.
-a few weeks ago I found an error code for the Intake Temp Sensor, but the code has not occured again after I cleared it.

While I provide care for a significant number of Volvos, I only work on a handful of Rex/Regina cars and this is a new issue for me on a Rex system. I'm looking for suggestions and ideas that fellow Brickboarders may have come across that they could share with me. Looking at the wiring diagrams, I've been unable to find any obvious areas to address that don't require swapping parts that I don't have, other than cleaning ground points again and resoldering relays for a 2nd time. I'm closely following the progress with Masupra's issue and his LH-2.4 Bosch system, but I still need to make headway on this car. I'm hoping and praying it's not the Rex-I Ignition Computer, as dealt with by Chrissij two years ago (see this linked post) as I don't have a spare REX-I ignition computer to experiment with without stealing one from another friends car (who needs to get to work every day). I'm looking at the 1994 Volvo Quick Reference Parts Catalog and I see that the REX-I ignition computer seems to have only one part number for all of it's 740/940 applications from 1989 through the printing date (part number 3507696) so it looks like I might be able to perform a parts swap with another friends 1990 740 Rex/Regina for experimentation purposes. Fortunately, it seems that the Igniton Coil with integrated Power Stage is also the same from 1989 through the printing date (part number 1367438). Anybody have experiences with failure rates or life expectancy of the Ignition Coils / Power Stages? -or are they pretty bulletproof?

At this point, my tenative plan is to do the following:
-Replace the RPM sensor again, just to see if I installed a faulty one last year when I changed it then.
-Unplug and reconnect all the electrical connectors to the Ignition Coil and it's built in Power Stage. (Herb mentioned that there is info available about cleaning/repairing this connection, and can be found on the Brickboard. I have been unable to find this info, please post if you you know where to find this information.)
-Clean the ground connections again.
-Last resort: Convince a friend to let me swap parts with his 1990 740 Rex system and see if the symptoms follow one particular part. (Ignition Coil & Power Stage, Ignition Control Unit/Computer, Air Temp Sensor, etc)

If you have any suggestions or thoughts, please post. I appreciate any help and advice. I need to get this problem dealt with as quickly as possible, since I don't have much spare time to deal with this right now. Higher priority issues are looming overhead (like my wedding in 5 weeks and all the stuff yet to be done for it).

Thanks for any help you can offer, and God bless.
Fitz Fitzgerald.