Hi Robert,

The long interval intermittent problems are the hardest to resolve.
Service the Air Mass Meter and CPS connectors.
Also service your PEM, including new thermal compound and use of Penetrox on the connector.

Doing this helped calm down a frequent intermittent in my 940 to the point where I was getting hopeful of a solid fix. But no, I got a code for sporadic or missing RPM signal (CPS).

Previous to this I suspected EMI/RFI corruption of the CPS signal and was surprised to find that the shielded cable for the CPS is un-grounded at the Bell Housing. This might be OK with new ECU's with their new electrolytic filter caps, but not so good with geriatric caps. So I added a pair of snap ferrites (RF chokes) to the CPS harness, one at the bell housing, and another near the harness connector.

I ordered some 28MM ID tinned copper braid for EMI/RFI shielding.
I plan to cover the plastic CPS connectors (NOT RF connectors) and find out exactly what size braid is the smallest that will pull over the connectors. I found out yesterday that the CPS harness has really crappy aluminum shield instead of braided copper found in a 2-conductor Belden mike cable for instance.
The old CPS I received measured OK 179.2 ohms but the sheath was falling apart
and the flimsy aluminum left it open to RF corruption to the RPM counter.
While I'm waiting for the braid to show up from China, I wrapped the CPS connectors in aluminum foil and black tape to add some shielding there.
It's ugly to look at but better than the lack of any shielding at the connectors. I expect to have this EMI braid in less than two weeks to do a better job of shielding the CPS harness and see if it resolves this vexing long term intermittent problem that was also bugging the previous owner of this 940.

EMI is not a new issue for cars, One Volvo TSB for a 240 ABS issue was to re-position the ABS harness that was acting like a tuned in antenna!

Good luck, Bill