Narrative:

We pushed back and started the engines. I told my first officer (first officer) to start both since we were heavy. After engine start I called for the after start check but the number one generator would not come on line. After a few seconds the idg (integrated drive generator) light came on. There was a strange vibration on the throttles. We called mx and headed back to the gate. I called for the number two engine to be shut down. This is where it gets weird. My first officer said number one was already shut down! I looked down and the left engine start lever was in cutoff. But number one engine was running and I still could hear and feel the vibration from it. We called ops and told them to let the ramp know we were using the number 2 engine to park (non SOP). We pulled into the gate and immediately shut down number 2. I opened my window and yelled down to the ramp that number one was running and I could not turn it off. Since the engine should have been shutoff and was not; I pulled the fire handle. Even after a minute or so the engine kept running! At this point the vibration was more pronounced; and noise was loud and getting worse. I was concerned about the passengers and ordered the flight attendants to de-board the aircraft (the jetway had arrived). The engine instruments showed N1 and N2 rotation; (lower than normal); a low egt (in retrospect it was probably residual; but it was high enough that I thought there was still ignition); and zero fuel flow. I did not trust the fuel flow gauge since I could hear and feel the engine running. The starter valve light was off and had been off since number one engine start. This next part is what I am concerned with. I fired the right fire bottle into the engine; hoping it may shut the engine down. I figured; at this point; why not! I saved the other bottle in case a fire warning occurred. My thought process was that I felt the situation was getting worse and that I wanted to get the people safely off of the aircraft; and that the fire bottle was something I could try. At this point we had 3 mechanics in the cockpit who were all as baffled as we were. The people all got off safely and the engine just kept running with very loud noises and vibration. Over the next 10 minutes multiple mechanics came into the cockpit and we all just kept staring at what was supposed to be impossible. One mechanic went downstairs and went behind the engine and determined there was no heat coming off the engine. He came back up and told us the starter valve must be open; but the light was out and the start switch had popped back to the off position. We shut down the APU bleed and the air came off the engine and it finally shut down. I think the starter must have run for close to 20 minutes. After the event; a mechanic started getting on me for blowing the fire bottle. He made a few statements. The gist of which were that I was going to be held responsible for unnecessarily discharging the fire bottle. I had so many things on my plate at the moment that I did not get his name. I got really concerned the more I thought about what he said. My thought process was safety of the passengers and the ground personnel; not monetary or labor costs. As we flew [another flight] my first officer and I talked about what happened; we could not figure out how the number one fuel shutoff lever went to cutoff. He was sure he started the engine and he did not remember touching the start lever after that. I never touch those levers. I have watched 7 engine starts since and I have determined that the engine idg light goes out around 45% N2. Max motoring is around 25% N2 so the engine had to have started. I definitely saw the idg come back on when I was trying to put the number 1 generator on the bus.it is possible that he did not get the start lever into the detent and the vibration from the start valve never closing (even though the start valve light went out) caused the fuel lever to slide back to cutoff. This is just a guess. My whole thought process in this incident was that the fuel valve was open and the indication of zero fuel flow on the gauge was wrong. As it turned out; the start valve was open and the indication (start valve open light not being on) was wrong.I have looked in the flight manual and learned that the start valve is upstream from the engine bleed valve and that pulling the fire handle will not cut off air to the starter. I will admit that I was really confused; along with the mechanics who were in the cockpit after we got back to the gate. I just tried to do what felt best to keep the passengers and ground personnel safe.

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Original NASA ASRS Text

Title: B737 Captain reported while returning to the gate; the left engine start lever was in cutoff but the engine continued to run. The Captain pulled the fire handle but the engine continued to run. Finally; after turning off the APU; the engine shut down. It was determined the start valve was open.

Narrative: We pushed back and started the engines. I told my FO (First Officer) to start both since we were heavy. After engine start I called for the after start check but the number one generator would not come on line. After a few seconds the IDG (Integrated Drive Generator) light came on. There was a strange vibration on the throttles. We called MX and headed back to the gate. I called for the number two engine to be shut down. This is where it gets weird. My FO said number one was already shut down! I looked down and the left engine start lever was in cutoff. But number one engine was running and I still could hear and feel the vibration from it. We called Ops and told them to let the ramp know we were using the number 2 engine to park (non SOP). We pulled into the gate and immediately shut down number 2. I opened my window and yelled down to the ramp that number one was running and I could not turn it off. Since the engine should have been shutoff and was not; I pulled the fire handle. Even after a minute or so the engine kept running! At this point the vibration was more pronounced; and noise was loud and getting worse. I was concerned about the Passengers and ordered the Flight attendants to de-board the aircraft (the jetway had arrived). The engine instruments showed N1 and N2 rotation; (lower than normal); a low EGT (in retrospect it was probably residual; but it was high enough that I thought there was still ignition); and zero fuel flow. I did not trust the fuel flow gauge since I could hear and feel the engine running. The starter valve light was off and had been off since number one engine start. This next part is what I am concerned with. I fired the right fire bottle into the engine; hoping it may shut the engine down. I figured; at this point; why not! I saved the other bottle in case a fire warning occurred. My thought process was that I felt the situation was getting worse and that I wanted to get the people safely off of the aircraft; and that the fire bottle was something I could try. At this point we had 3 mechanics in the cockpit who were all as baffled as we were. The people all got off safely and the engine just kept running with very loud noises and vibration. Over the next 10 minutes multiple mechanics came into the cockpit and we all just kept staring at what was supposed to be impossible. One mechanic went downstairs and went behind the engine and determined there was no heat coming off the engine. He came back up and told us the starter valve must be open; but the light was out and the start switch had popped back to the off position. We shut down the APU bleed and the air came off the engine and it finally shut down. I think the starter must have run for close to 20 minutes. After the event; a mechanic started getting on me for blowing the fire bottle. He made a few statements. The gist of which were that I was going to be held responsible for unnecessarily discharging the fire bottle. I had so many things on my plate at the moment that I did not get his name. I got really concerned the more I thought about what he said. My thought process was safety of the passengers and the ground personnel; not monetary or labor costs. As we flew [another flight] my FO and I talked about what happened; we could not figure out how the number one fuel shutoff lever went to cutoff. He was sure he started the engine and he did not remember touching the start lever after that. I never touch those levers. I have watched 7 engine starts since and I have determined that the engine IDG light goes out around 45% N2. Max motoring is around 25% N2 so the engine had to have started. I definitely saw the IDG come back on when I was trying to put the number 1 generator on the bus.It is possible that he did not get the start lever into the detent and the vibration from the start valve never closing (even though the start valve light went out) caused the fuel lever to slide back to cutoff. This is just a guess. My whole thought process in this incident was that the fuel valve was open and the indication of zero fuel flow on the gauge was wrong. As it turned out; the start valve was open and the indication (start valve open light not being on) was wrong.I have looked in the flight manual and learned that the start valve is upstream from the engine bleed valve and that pulling the fire handle will not cut off air to the starter. I will admit that I was really confused; along with the mechanics who were in the cockpit after we got back to the gate. I just tried to do what felt best to keep the passengers and ground personnel safe.

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.