Reviving an old thread as I am still experiencing this problem. Still don't drive it as much as it is the wifes daily driver, but had it for the weekend for a road trip and was able to monitor engine info along the way.
Via accelerator, 75 mph flat interstate, RPMs stayed constant 1900 RPM +/- 10, fuel rail pressure constant ~ 2000 psi, MAF cfm remained constant.
Via cruise control, 75 mph flat interstate, RPMs stayed constant 1900 RPM +/- 10, fuel rail pressure would fluctuate between be at ~2000 psi then drop to 1500 psi up to 2400 psi during periods of felt surging. MAF cfm would also fluctuate at the same time.
So it has to be tied to the cruise control system some how. Anyone know exactly how the system works and/or what could be causing the issue?