Engine idling gone crazy

there is an idle up solenoid on the the carburetor. adjust the idle speed at 800-900rpm. RPM up and down is due to a/c compressor engaging. if the rpm drops too low, a/c compressor disengages. observe your idle speed with engine warmed up, turn on airconditioner and adjust the idle compensating vacuum diaphragm adjustng screw underneath the carburetor to the same rpm when a/c was off. that should correct your rpm problem

so what works and what not.
so far we have cluster issues
does car drive, ok day and night.
and all accessories?
did engine stall driving?
did Head lights dim? on, driving?
my guess is the engine stalled or idled below 300rpm
and the ECU went to Key on self test mode, (they all do that)
watch the RPM guage? see that needle, ?
if it goes below 300 rpm that is engine stall.
or worse
This cars cluster is really just a digital display
so if the PCM cant talk to the cluster, the cluster will go nuts.
for freeze.
We use a scan tool to see whats up.
or use the cluster self test covered in the shop manual.
the cluster has 2 fuses that can be cracked/loss or corroded.
the cars battery can go weak.
if the charge/battery light glows, engine RPM good
then the alternator systems is failing
if the volt meter (if opted) in cluster drops below 14v, and engine is still running, the same, alternator system failure
or even a loose belt at the alternator.
if the battery voltage drops too low , all electrics go nuts.
and engine stalls.
what dies first with low battery , is luck of the draw....
so what was battery voltage
and engine RPM at the point of failure.??????????

What's happening is, the engine is under increase load when the A/C is running. Typically there is a solenoid (near the throttle linkage) that controls idle speed when the A/C compressor (clutch) is engaged. It activates each time the compressor cycles on to regulate the system. If idle returns to normal when A/C clutch is disengaged (or A/C is off), then the solenoid or some signal that controls the solenoid to maintain the idle is the likely to be the problem. e.g. The solenoid fuse maybe blown. This might be a good place to start investigating the problem. Best of luck resolving this problem.

have the fault codes read and fix the faulty sensors

try to reset the computer if that doesnt work reset the idle speed it may have picked up bad codes

Before anything is done to the AC, have the throttle body cleaned. A dirty throttle body will cause engine RPM to drop or even stall.
What makes you think the compressor is seized? Does the compressor pulley spin when AC is engaged? If compressor was seized the pulley would not move and belt would squeal.

The idle air control valve is what regulates incoming air when the engine is idling. In some cases these can malfunction and cause intermittent issues with stalling at idel until the IAC dies altogether.

buffalo man said engine doing what it should do. friendly neighborhood mechanic said it go 1250 RPM on start up, then drop to 700 to 800
found defective part outside throttle body. runs OK now

Drive it to Autozone or similar place and ask them to scan the car because the "check engine light is on". Most likely it will be a TPS switch. In area of $30 for part. It takes about 20 minutes to do. Most of time spent getting to part. But see what scan shows.

Sounds like a bad IAC (idle air control valve/sensor) that controls your idle when going from throttle to idle. If bad your idle will act crazy and can cause stalls easily. Pretty sure that's it.