1992 Buick Regal my wifes Buick

The first step is to read and record any diagnostic fault codes. The people at many auto parts stores will do that for you for free. Be aware those codes never say to replace parts or that one is bad. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition.

Please forgive me for not paying attention to the year. '95 and older cars each have their own methods, and each brand is different. You can read the codes yourself:

https://www.2carpros.com/articles/buick-cadillac-chevy-gmc-oldsmobile-pontiac-gm-1983-1995-obd1-code-definitions-and-retrieval-method

Only Chrysler is easier. You just cycle the ignition switch, but the codes are read the same way.

23 - Intake air temp sensor out of range, low

Don't even waste your time suspecting this sensor is bad. It only has one component inside, a "thermistor", or temperature-dependent resistor. I tried to install a "bug" into a donated car for my students to diagnose, and there's nothing that can be done to make it cause a problem other than to cut one of its two wires. Doing so, either inside the sensor or in the wiring harness going to it, will cause code 25 to set:

25 - Air temp sensor out of range, high

And you'll notice neither code says to replace it. To get a "low voltage" code 23, the two wires have to be shorted together, or the signal wire has to be shorted to ground. The things to look for are excessive corrosion between the sensor's two pins in its connector, or its signal wire has rubbed through somewhere and is touching a bare metal part of the body or a bracket on the engine. You can verify the sensor is okay by measuring its resistance. Most will read somewhere in the area of 500 to perhaps 10,000 ohms. The resistance will go down as the temperature goes up. Basically all you care about is it doesn't read 0 ohms or open circuit.

A mechanic's next step would be to connect his scanner to view live data and see the voltage on the sensor. It is fed with 5.0 volts, then the sensor draws that voltage down based on temperature. The acceptable signal voltage range is between 0.5 and 4.5 volts. As long as it stays within approximately that range, no fault code will be set.

The next step is to measure the signal voltage at the sensor, (with it still plugged in), and compare that to the scanner's reading. If they're different, suspect a cut wire.

I read a lot about people assuming that refers to an Engine Computer problem, and of course the code will go away if the computer is replaced, but it seems to be much more of an issue of setting false codes in response to something else. I would erase the codes now that you know what was set, by disconnecting the negative battery cable for a minute, then see if either of them set again. I'm betting code 26 won't.

Again, fault codes never say to replace a part. They tell you which circuit to diagnose. For the next vehicle you should start a new question so the people who specialize in emissions issues will get to see it and have a chance to reply. Be sure to include the year and engine size. Double-check that code number. Code 36 has something to do with the ignition system, not the EGR system.

The only thing that might happen is air would pool under the thermostat, and that's where coolant temperature sensors live. If the sensor for the Engine Computer reads a temperature that's too low, that might send the system into "open loop". Fuel metering calculations will be based on the readings from all the sensors except the oxygen sensors. That shouldn't cause a running problem, but that's not a normal condition either, so it's hard to say. The clue would be if the running problem goes away when the cooling system is full.