Date: 201703
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Light: Daylight
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Takeoff / Launch
ATC / advisory: Tower ZZZ
Aircraft component: Turbine Engine
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Rejected Takeoff
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Aircraft arrived with open maintenance item of wing anti ice valve open. Dispatch elected to have maintenance keep valve open and have MEL added to our release. We started #2 engine at gate with maintenance representative on board. Left the gate and performed a cross bleed start for #1 engine. Upon taxi out I elected for a 26;000 max power takeoff and my FO pulled up a new takeoff performance via ACARS. While taxiing we were cleared for takeoff. The remainder of the before takeoff checklist was completed and I was the designated PF. I elected to make a rolling takeoff. I advanced the throttles to 40% as I was still in a left turn to align with runway heading. I believed I saw both engines stable as I engaged the auto throttle button. Immediately the left engine went to max power and the right engine did not respond. I could not get the aircraft aligned with the runway with rudders and nose wheel steering. The aircraft began drifting toward the right side of runway as I closed both throttles to idle. Max manual braking was engaged to keep aircraft on runway. As the aircraft slowed down I regained steering control and continued taxiing down runway to next exit spot. Max speed was approximately 40 kts. Spoilers and reversers were not deployed. An emergency was NOT declared. Aircraft was taxied back to gate and taken out of service. Factors that contributed to event: 1) Maintenance and MEL procedures that were non-standard and a little confusing for both maintenance and the cockpit crew. 2) First leg of three legs and we were already delayed with the maintenance item. We knew we were in for a long day and this was only making it longer. 3) Failure to properly recognize if both engines were in fact stable at 40% prior to engaging autothrottles. I cannot remember if I verified if both engines were in fact at 40%. Although I have done many rolling takeoffs in my career; this was more dynamic than any others. Procedurally; I was felt I was doing everything I had done previously. When the left engine went to full power; my focus was outside trying to align the aircraft with the runway centerline. As the aircraft was pushed further right; I countered with more nose wheel steering and left rudder. I was slow to recognize the power difference in the engines. The aircraft just pushed the nose wheel even with full left deflection. It wasn't until I went to idle and full brakes that the airplane slowed and I regained steering control. Obviously there was a problem with the #2 engine. I think this would still have resulted in a rejected takeoff in any scenario. It would have probably been less dynamic if it was not a rolling takeoff. I also think it would have been less dynamic if I had ensured both engines were at 40% prior to engaging the autothrottles; again; I cannot remember what I saw before engaging them.


Second narrative: [Report narrative contained no additional information.]


Synopsis: B737 flight crew reported an asymmetrical power situation as the autothrottles were engaged for takeoff resulting in a rejected takeoff.