Why does my car start/stall unless I am giving it gas after I changed my manifold?

Check for vacuum leakages for the low idling.
As to the A/C etc not working and overheating, have you checked the fuses?
Did you miss out any ground circuit connections?

Ground circuits are bolted to some part of the engine so if any was disconnected while removing bolts, they could have been missed out.

As to the overheating and A/C not working, it could be a blown fuse so did you check as I suggested? Sometimes jumping the gun makes you go round in circles. Always start with the basic. A blown fuse would prevent the cooling fans from working and this would result in overheating and tha A/C not working. Btw recheck the wiring connectors that you disconnected. Check if any had been interchanged. Note the wire colors.

You mentioned disconnecting the battery. That can result in low idling as computer memory is erased and needs to relearn. During this time the idling would not be stable and might stall. One way of expediting it is to get the throttle body cleaned to eliminate air flow restriction due to dirt accumulating.

Lol. I read it as the battery was disconnected. For the temp gauge not working, I understood it as a typo and understand the situation.

Have you checked the fuses?

Let us start with the basics. Temperature gauge first. The attached schematic shows the temperature sending unit wiring. Unplug the connector and use a wire to ground the Red/White wire. Turn ignition switch on and if the gauge works, either the switch or ground circuit is bad. If gauge works, do not keep ignition switch turned on for more than 3 seconds.

Why don't you want to answer my question?
If you do not want to answer, I would not be able to help you.

I keep asking if you have checked the fuses. If there are any pinched wires, the fuse would blow or the temp gauge would shoot to maximum.

Without knowing the problem how would you expect me to answer you. You mentioned there were no witres around so how can you have a pinched wire? You did not ask me if it is possible, You kept saying others have told you so. If you don't want to do it my way, the you would have to get somebody else to do the job.

Have a nice day.

A blown fuse can cause all these and you refuse to start with the basic.

Sorry to say I am not able to assist you further.

All we're trying to do here is help people in need of car repairs being uncooperative will not help here, reading it all I suggest you go somewhere else and seek help-You came here for a reason-

FYI, disconnecting the battery is a bad idea-there's a way to keep the computer memory alive at all times-Do you know this?

Hi Jess, welcome aboard.

Lol. Thought I was the one who read the question wrong. Seems you too read it wrong. The battery was not disconnected.

What's this? The only thing I did that wasn't by the manual was disconnect the battery.