Aircon cuts out at idle - Land Cruiser Toyota Cars & Trucks

you don't adjust the idle for any accessories
The idle is set for smooth running of the engine( normally 750-900 rpms with a drop of 200-300 rpms with an ac running so set the idle at the upper rpms and it will still be smooth when the ac is on without affecting gear engagement
your problem I take it is that when the ac cuts in the idle rpms drops and makes the engine run rough
This is normal as the ac compressor takes up to 5 hp to drive it
what you need is an electric controlled vacuum pot connected to the accelerator lever so that when you switch on the ac the power to the ac clutch energizes the pot and vacuum pulls the accelerator lever to maintain the set idle rpms
such an item is found on most early carby operated engines

That is most likely caused by the Idle Air Control solenoid.

Sounds like the compressor is failing or seized (for the air con). This would put extra pressure on the system. It could be another fault with the air con system like the solenoids not opening up to allow the flow of gas in the system.

Engine stalling issue at low speeds

This problem is commonly caused by a dirty automatic idle speed control valve and throttle valve. Buy a can of throttle valve cleaner from NAPA or Carquest (made by CRC chemicals) and spray it into the air intake while the engine is running, use up about 1/2 the can, engine will try to stall hold the speed up, shut it down and let it soak for 30 minutes, restart and blow out the remaining fluid, shut it down and disconnect the negative battery cable for 5 Min's to reset the base idle control

this means that your idle when the aircon is off is very low. basically there are 2 adjustments for idle: engine idle and aircon idle. just try to locate this screws in your engine. set the engine idle at 700-800rpm, while the aircon idle at 900-1000rpm.

When the aircon is switch on it puts a substantial load to the engine: you need to get your car tuned to take into account the load from the aircon. Most car have a mechanism that increases the idle speed when the aircon is active: if you are unable to get your car tuned yet, try making the engine idle speed slighty faster while you have the aircon turn-on (the ajustment screw should be close to the accelator cable connection at your engine end). Don't make the idle speed too high and check by turning the aircon off and on to assess the best compromise idle speed to stop your car from almost stalling (e.g. jerking).

Good luck!

manual or automatic?

hi, you my check vacuum connection,specially the idle compensator. it should work by increasing the idle when aircon is on.

There may dirt or rust in idle air passes
Service & adjust the Idle speed control valve & throttle position sensor.

dude its normal for first start or cold start that the idle is ok but it must high than normal... its normal because the engine is warming up it self... when it gets warm, the idle speed will return normal idle... your engine is 1200cc, it has not much HP for a great load... and i know its a carburatored engine and its an old engine, your head lyt and a/c fan and aux fan and all the electrical system on your car, uses the HP of you engine and its a lot of load to the alternator driven by the engine to generate an electricity they need and thats why the engine rpm speed lowering down to dead and its shake. thats why when you use your lyts or all electrical, you engine is weakening... the best remede is adjusting you idle speed... its located behind the carburator.. its a small black knob.. just make a twist each eighter way and you'll find out if your idle rpm speed ts incresing or decresing.. just increase it and try opening your lyts and other electrical, if its still shaking then adjust it a little more