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I think you are on the right track with the ecu! I would rec to try and pull codes with a scanner. YOu local auto parts store may be able to do this for free for you. Let me know.
Maybe you would like to try to pull codes again and see if that helps. Would you like the procedure on pulling codes?
Here is the info on pulling codes if you want to try it again.
READING DIAGNOSTIC CODES The Electronic Control Unit (ECU) monitors several engine sensors and actuators. If a problem occurs the information is stored in the ECU's memory for retrieval.The codes are displayed by the green and red diodes on the ECU. When the codes are extracted they are interpreted by the number of times the diodes flash.The red diode will flash "X" number of times, this will represent units of ten, then the green diode will flash "X" number of times, this will represent units of one.For example, if the red diode flashes once and the green diode flashes twice this should be interpreted as code 12. The codes are displayed in numerical order starting with the lowest and ending with the highest.EXTRACTING DIAGNOSTIC CODES