Ok so I just tried this again and was able to push the diaphragm. The car shut completely off. I did it twice, same thing. So does this mean the EGR is good? What should I do now?Yes, that’s it. Look at the EGR in your second photo. If you put your finger into it, in between the metal ‘spokes’ that you see in the photo, you will feel a metal bit inside there. You will not be able to push it forward unless the engine is running. You need to do the test with the engine warmed up, so be careful not to burn your fingers when doing this - gloves or some other protection is good - don’t use anything sharp, as if you miss the metal inside the valve, you can puncture the diaphragm.
I put back the old serpentine belts. I thought it looked good still. I’ll order new ones and this time I’ll try to use a lever instead of forcing it on.Most probably as your belt is new, it’s that the tension is not tight enough. When you press the belt inward, normally to the right side of the fan as you are standing in front of the car, it should only press in about 1/4 inch of so. I don’t have the A/C, but I know that in order to get the alternator shifted over far enough to have the belt properly tightened, you normally need to use a lever of some sort, rather than just trying to do this manually. It can be quite difficult to shift the alternator.