Narrative:

During preflight looking at the logbook; it was noted several times that this particular plane was having some issues with the engines specifically. Both the first officer and I looked at it and made a mental note. We also went over the 4 MEL's we had on the plane and the one most affecting us was the auto-throttles being out. Once we went through each MEL we continued on our normal preflight duties. There was a discrepancy with the passenger count and also the flight plan fuel numbers were not matching up with the FMS flight planned numbers. The FMS had calculated that we would land in ZZZ1 with roughly 4100 pounds of fuel while the paper work planned us to land with 4824 pounds. This disparity was because at one waypoint; the flight plan had us crossing the point with 13715 pounds of remaining fuel while the FMS had us crossing the same point with 13100 pounds. I called the dispatcher and we went over each point on the flight plan to make sure we were all on the same page. After we concluded that there was adequate fuel; we pushed back and were on our way to ZZZ1. At roughly 15;000 feet in the climb out our engine 2 psi dropped from 75-80 and went to 30-33 psi. This is over a 50% drop in psi. An amber box illuminated the psi and there was also an associated rise in the vibration for engine 2. The vibration was still within limits at roughly 3.2; but was very clearly audible in the cockpit that the higher vibration in the engine was causing the engine to perform differently from engine 1. This condition lasted for roughly 2 minutes. During this time; both the first officer and I were aware of the problem and started talking about it. I was pilot flying so I instructed him to ACARS dispatch and maintenance about our current situation. We gave a status report of the engine psi along with the elevated vibration. They responded with something to the effect of 'mx is aware. Copy thanks.' after those 2 minutes; engine 2 went back to indicating normal psi and lower vibration where we could not hear anything. That homeostasis lasted for another minute before engine 2 psi dropped down again with an associated rise in engine vibration. This was now the second indication of getting an erratic with the engine and we were still within 100 miles of ZZZ. At this point; the first officer and I were not comfortable with continuing the flight another 2.5 hours to ZZZ1 or roughly 1200 miles. We asked ATC for a level off so we could trouble shoot the problem. We ACARS'd dispatch/maintenance and again updated them on our situation and their response was something to 'run the appropriate QRH'.at this point we asked ATC for box vectors for a possible return to ZZZ. We opened up the QRH and went to low oil press 6.7 in our book. That was boxed in red but was associated if we were actually getting the engine 1(2) oil lo press EICAS message. We were not getting that message. However; our psi was not far from this possibly being an emergency. The QRH again for engine 1(2) oil lo press tells you that the oil pressure indication is abnormal and you should go to engine shutdown procedure. We flipped to this section of the QRH and it says to review single engine performance and the second bullet point is to land as soon as possible. At this point; we as a flight crew decided it would be best to return to ZZZ. ATC asked is we wanted to return to ZZZ and we said yes and we started getting vectors appropriately. We ACARS'd dispatch/maintenance about our decision and they were very helpful coordinating with operations letting them know we were returning and getting us gate space. We called back to the flight attendant's and then I made an announcement to the passengers explaining the situation and why we would be returning to ZZZ. Once we made the turn back to ZZZ; we were roughly 100 miles away. We elected to keep engine 2 running because at this point it was giving us good indications and we concluded that as long as it was giving us positive thrust; the prudent move was to keep it running. Also we talked with dispatch/maintenance about landing overweight. Max landing weight was roughly 74;000 pounds and we were 78;000 pounds. ATC vectored us onto the arrival into ZZZ with a visual approach. We landed and taxied back to our gate and thus completed the flight. During the debrief; we went over the situation again how the engine had given us 2 erratic indications and how we were confident that returning to ZZZ was the safest choice. I commended my first officer and cabin crew for their calm attitude during the whole ordeal and then coordinated with maintenance for applicable write ups and coordinated with crew scheduling about our switch in schedule.

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Original NASA ASRS Text

Title: EMB-175 flight crew reported returning to their departure airport because of oil pressure and vibration problems with Engine 2.

Narrative: During preflight looking at the logbook; it was noted several times that this particular plane was having some issues with the engines specifically. Both the FO and I looked at it and made a mental note. We also went over the 4 MEL's we had on the plane and the one most affecting us was the auto-throttles being out. Once we went through each MEL we continued on our normal preflight duties. There was a discrepancy with the passenger count and also the flight plan fuel numbers were not matching up with the FMS flight planned numbers. The FMS had calculated that we would land in ZZZ1 with roughly 4100 pounds of fuel while the paper work planned us to land with 4824 pounds. This disparity was because at one waypoint; the flight plan had us crossing the point with 13715 pounds of remaining fuel while the FMS had us crossing the same point with 13100 pounds. I called the dispatcher and we went over each point on the flight plan to make sure we were all on the same page. After we concluded that there was adequate fuel; we pushed back and were on our way to ZZZ1. At roughly 15;000 feet in the climb out our ENG 2 PSI dropped from 75-80 and went to 30-33 PSI. This is over a 50% drop in PSI. An amber box illuminated the PSI and there was also an associated rise in the vibration for ENG 2. The vibration was still within limits at roughly 3.2; but was very clearly audible in the cockpit that the higher vibration in the engine was causing the engine to perform differently from ENG 1. This condition lasted for roughly 2 minutes. During this time; both the FO and I were aware of the problem and started talking about it. I was pilot flying so I instructed him to ACARS dispatch and Maintenance about our current situation. We gave a status report of the engine PSI along with the elevated vibration. They responded with something to the effect of 'mx is aware. copy thanks.' After those 2 minutes; ENG 2 went back to indicating normal PSI and lower vibration where we could not hear anything. That homeostasis lasted for another minute before ENG 2 PSI dropped down again with an associated rise in engine vibration. This was now the second indication of getting an erratic with the engine and we were still within 100 miles of ZZZ. At this point; the FO and I were not comfortable with continuing the flight another 2.5 hours to ZZZ1 or roughly 1200 miles. We asked ATC for a level off so we could trouble shoot the problem. We ACARS'd dispatch/maintenance and again updated them on our situation and their response was something to 'run the appropriate QRH'.At this point we asked ATC for box vectors for a possible return to ZZZ. We opened up the QRH and went to LOW OIL PRESS 6.7 in our book. That was boxed in red but was associated if we were actually getting the ENG 1(2) OIL LO PRESS EICAS message. We were not getting that message. However; our PSI was not far from this possibly being an emergency. The QRH again for ENG 1(2) OIL LO PRESS tells you that the oil pressure indication is abnormal and you should go to Engine Shutdown Procedure. We flipped to this section of the QRH and it says to review single engine performance and the second bullet point is to LAND AS SOON AS POSSIBLE. At this point; we as a flight crew decided it would be best to return to ZZZ. ATC asked is we wanted to return to ZZZ and we said yes and we started getting vectors appropriately. We ACARS'd Dispatch/Maintenance about our decision and they were very helpful coordinating with operations letting them know we were returning and getting us gate space. We called back to the FA's and then I made an announcement to the passengers explaining the situation and why we would be returning to ZZZ. Once we made the turn back to ZZZ; we were roughly 100 miles away. We elected to keep ENG 2 running because at this point it was giving us good indications and we concluded that as long as it was giving us positive thrust; the prudent move was to keep it running. Also we talked with Dispatch/Maintenance about landing overweight. Max Landing Weight was roughly 74;000 pounds and we were 78;000 pounds. ATC vectored us onto the arrival into ZZZ with a visual approach. We landed and taxied back to our gate and thus completed the flight. During the debrief; we went over the situation again how the engine had given us 2 erratic indications and how we were confident that returning to ZZZ was the safest choice. I commended my FO and cabin crew for their calm attitude during the whole ordeal and then coordinated with Maintenance for applicable write ups and coordinated with crew scheduling about our switch in schedule.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.