I assume you have no codes? If we have not checked, let's start with that.
If there are no codes then if this happens at the switch to closed loop then we have to assume we have a sensor issue. The sensor that would make sense is the upstream o2 sensors as most other are used during open loop as well but are run off a default program. I attached some info about this.
The best thing to do is monitor the o2 sensor data to see what it is telling the PCM. Then check the short term fuel trims and see if that is telling us something different. Since you already changed the ECM and sensors, it could be a wiring issue. However, let's see what the codes say or what the o2 are reading and go from there. Thanks
Saturday, August 1st, 2020 AT 6:45 PM