2002 Toyota Celica GTS P1300-P1315 codes

So my son has a 2002 Toyota Celica GTS that continues to throw P1300, P1305, P1310, P1315 and P0300 codes after about 15 to 20 minutes of driving or also noticed when on moderate right hand turns it also seems to misfire. We took it to the dealer and his recommendation is to replace the ECM. They did run several tests and cleaned up a ground but the problem persists after a different ECM. Another shop currently has it but hasn't found anything in the loom so far. From what the dealer stated, Found ECM connector e5 pin 25 for ignition field losing 5v reference. Replaced Coil Packs and spark plugs, o2 sensors, oil pressure sensor and a coolant temp sensor. another interesting piece of information is that when I replaced the ECM, it appears that there is a group of brown wires in that ECM box that isn't connected to anything. From the looks of the end piece, it looks like it may go into the blue connector that is to the side of the ECM and appears to be ground wires but not sure. I don't think the Dealership caught that and my son just reminded the current person that is looking at the vehicle about those wires. I don't have a diagnostics computer so limited on what I can do but I do have an ODB reader and voltmeter. Has anyone happened to run across a crazy electrical problem like this? Do you know of anyone in Indiana (preferably Greenwood but willing to go wherever to get this fixed) that has gone through your course that could be of assistance?

look at your igniter circuit

All the coils share a power supply which is also shared with the injectors.
All the coils share a ground.
The IGF signal from all the coils are spliced together and run back as a single wire to pin on the engine computer.
With ignition on the IGF signal is 5v which pulled down to zero volts as each coil is charging. so you get a 5v square wave
A short in any of the coils or the wire carrying the IGF signal back to the ecu could cause the symptoms you describe.

So do you think those 4 brown wires (in the attached pic on orig post) are part of the grounding for the Coils or injectors. It looks like from the end that is on those wires, it might have came out of that blue connector where the ECM is. But I haven't been able to get clarification from some of the manuals that I've found. Still searching though.

The ground side of that circuit was the initial culprit. 45 dollar fix new negative ground wire and a grounding kit fixed the full issue. traced the ground point for the coil packs and it was corroded and gunked up. so then I check some of the other ground points. In all, cleaned up about 5 or 6 ground points especially the initial grounding points from the battery which that cable was heavily oxidized and corroded. ended up adding a grounding kit to help out the ground points even more for this 17 year old car. Took several right turns and took on a long drive and didn't have a single bit of problems. Yay! Thank you all that have helped. Moral of the story, check ground points if sensors check fine but are still having drops on reference signal. it's a quick and cheap check to mark off the list. especially on older vehicles

Unbelievable the amount of parts that were literally thrown at the car. Our industry is just absolutely awful. There are very few shops that know how to troubleshoot. Ridiculous.
Wish you would have come here first @wcain143 but at least you fixed it! Nice job.

that's why I have to keep pressing getting better but its been hard but I refuse to be a parts changer I believe there is a select group with skills of excellence in diagnostics thank you for your instruction

Hellos I’ve having this same issues. Do you think you could walk me through exactly what you did?