Friend with a CM870 having issues

[8042]

I haven’t posted in a long time, but have a friend that is having issues with his intact CM870.
He has had problems joining so asked me to post this. I have to admit it is over my head.

Gents,
I have a 2006 Volvo VNL780 with a Cummins ISX15 500 cm870 (egr original)with an Active fault code of 2554 (Insite). In other words, "erratic data" (inactive) and "electrical fault" (active) from the exhaust gas pressure sensor. Upon cold start, engine rpm surges up and down about 200rpm in a rhythmic cycle.
Went to International, got a new exhaust gas pressure sensor, installed it, great. It worked ... for a week. Surging starts once again, and code 2554 comes up again. Measured resistance on the EG pressure sensor and had all reading of infinite ohms across pins 1 to 2, 2 to 3, and 1 to 3 (all open). Ok, figured new sensor was faulty.
Went back to International and got a replacement sensor. Measured resistance of 4.5kOhms on pins 1-2, and 68kOhms on pins 2-3, while pins 1-3, open. Also, checked continuity between ECM harness and exhaust gas pressure sensor: ECM pin 37->1, 47->2, 20->3, all zero ohms. Installed sensor, and all seemed well for another week. Then, surging started once again.
Again, checked resistance of sensor as well as harness continuity, with all values being the same as stated above.
Hooked up to Insite, and noticed that exhaust gas pressure reading was at 48inHg while barometer (ambient) pressure was at 30.2inHg, with engine OFF, key ON.
To my understanding ,the exhaust gas pressure sensor is an absolute reading and should read close to barometric pressure sensor values. However these readings are very different.
Questions:
1) Is it possible that second exhaust gas pressure sensor is a dud? Or are International sensors different in any way? International claims it is the correct sensor (Cummins Dealer)
2) What should the resistance be of the sensor (is this relevant /irrelevant)?
3) Why can't I win the lottery?
.... hmmm