AT Check light after Code P0507 ISC?

Hello, there is a Technical Service Bulletin on this issue, which Ill post but the throttle body will not relearn if the rpm is even just 25 RPMs higher than it should be at idle, I'm not sure what that bang noise is, but it's extremely loud even in the video. I assume the vehicle might be in some Limp Mode or Reduced power mode right now. But I'll post this TSB, it actually has you unplug a fuel injector to lower the rpm so the throttle body can relearn.
But retrace your steps from the spark plug change and injector testing, make sure you don't have any loose hoses or lines that are causing a vacuum leak, which will raise the RPMs. I don't think the throttle body is the issue, with this spec of only 25 RPMs, that is not much of a range for it to be out of spec. You may consider putting the old throttle body back on and see if it will be ok without having to relearn the old one. You can also try a smoke test on the intake manifold and see if there are any air leaks, I probably wouldn't be driving it until you get throttle code taken care of, that noise sounds really bad. Do you have a scan tool that can scan other modules in the vehicle? Try doing a full system scan of the entire vehicle and see if there are trouble codes set in any other modules.
The AT module might be shifting like that if it doesn't know the correct rpm, the ECM may be sending it incorrect data.
Another issue with older vehicles like this is when you do any repairs which require moving the wiring harness around, there might be a connector that is not seated correctly right now, so retracing your steps and going back over everything you may have moved during the repair is a good idea, I run into this with older vehicles as well, the wiring harnesses get so brittle and due to so many years of being heated up and cooled down, the connectors expand and contract so much that when you go and unplug something to get it out of the way, you can end up with pin fitment issues when plugging them back in.
When a code sets that wasn't there before a repair, that's the first thing I go over, is what did I move or unplug that might have issues now. It has to be something you did if the issue wasn't there before, it happens all the time. So put the old throttle body back on with a good gasket and recheck the area you worked in.

https://www.2carpros.com/articles/engine-idles-too-high

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Hello,

Okay, so, when the warning light is on, it shifts hard to the next gear until you're at cruising speeds? Just trying to get an idea of what you mean by "large shock".

When you changed the spark plugs and this issue started, what brand plugs did you put in and what kind of testing did you do on the fuel injectors? I'm only asking because it looks like the TCM is going into failsafe mode for a short time (while the A/T lamp is on), and then coming out of failsafe mode. And if it is happening when you are coming to a stop, or slowing down, low speed and lower rpm, I may have an idea of what could be happening. I'm looking up some more info on why that warning light comes on right now, and I think we need to go back to when the problem started.
I can see why it's not setting any codes, with the light coming and going, the TCM or PCM is seeing the issue and then not seeing the issue, so it's not enough full drive cycles to set a code. Once you get moving again the problem disappears, so no code is triggered.

So, the AT light should come on for about 2 seconds at Ignition switch On, but does it happen to flash at all during the fault time, for about 8 seconds?
And it looks like the shock, or slam into gear you're experiencing is because when the TCM goes into its Fail Safe mode for that short period of time the TCM will stay fixed in whatever gear you happen to be in at that time, so when you accelerate and come out of Fail-safe mode, it might be going from that fixed gear into whatever gear it should currently be in for that speed and RPM.

Okay, thanks for that info. I think what is happening is something (like an ignition coil) is interfering with one of the sensors in the transmission, (ie vehicle speed sensor, Turbine Revolution Sensor 1 or 2). Since this started happening when the plugs were changed, and the coils were disturbed. I have seen in many situations like this where some weird intermittent issue happens only a certain rpms or certain engine loads, that it seems to always be an ignition coil spiking the ground circuit and causing a glitch in a sensors signal that does this. And it's because the coils are the component on the vehicle that have the highest voltages when they are firing. Sometimes it doesn't even need to be a really bad coil, it can be just a little high resistance through a spark plug that causes the coil to end up firing outside the cylinder to ground.
It will usually show up when scoping the vehicles power feed and ground to the coils that a voltage spike will be seen. With no codes and this weird issue happening, that's what I would check, since the problem can be duplicated pretty easily it sounds.
Can you graph and transmission live data PIDs with your scan tool? And see if you notice a speed sensor either dropping out, or reading incorrectly when the fault occurs?

I was looking at the wiring going to the transmission today and I see pins 5 and 10 are grounds, so you're saying you measured voltage drop from pin 10 to Battery negative when the fault occurred? If that's the case and that ground location is F11 "Front of Engine" and both pin 5 and 10 ground there, Id check for voltage drop from the engine block to battery negative and then also from the transmission case itself to the engine block, and the trans case to battery negative and see how much there is during the fault, because the transmission housing itself acts as a ground as well, it's not just the wiring going into the valve body.
If I remember correctly, there was a case where the transmission and engine block had voltage drop between them even though they were bolted together. Very strange one, I can't recall what the actual fault was, but it seems like almost anything is possible sometimes. Here are the wiring diagrams for the transmission. Check the pin tension for the transmission connector as well, it strange to have voltage drop like that at lower rpm, or speed. And why after only changing plugs.

That's really great, so it was the connector for the crankshaft position sensor?

Good find, it's always strange what loose pins will, I'm surprised it didn't do anything at higher RPMs, but anyway glad it's fixed. That was a strange one for sure.