Wayne when ever i turn my air conditioner on my idle goes way down.

check the automatic idle control valve. It might need to be cleaned.

This is a common problem especially with 4 cylinder engines when they are not in good tune, such as needing plugs. The computer can only do so much in maintaining the engine's power. The air conditioner compressor can also be a problem if it is overcharged. I've seen the compressor lock up and smoke the belt. A rough engine idle usually only happens when the car is at an standstill and it goes away when underway.

Disconnecting the battery will not delete stored fault history. It must be done with a CRT (Snap- On 3000) or equivalent. The idle condition you have now should be the opposite. 1200 RPM with air on 900 with air off. This vehicle is at an age where several components are probably out of range. I would try changing the cheapest parts first. 1 Fuel filter 2 Air filter 3 Thermostat For Coolant) 4 All coolant temp sensors (They can affect idle) 5 MAP sensor(manifold absolute pressure sensor) 6 Idle air motor. Sometimes the idle air motor can be cleaned . Check pintle and seat for carbon build up, clean with a valve guide brush. Pintle not seating will cause idle problems

sound like engine coolant temperature sensor faulty also coolant level too low.

When you place your controls on defrost it turns your air conditioner on - depending what the heat level is set on the air conditioner will cycle on and off to regulate temp. Anytime the A/C runs the idle sensor will bring the idle up

make sure both fans are running and that the idle air controller valve is not stuck

Check the cooling fan switch. It appears your auxiliary electric cooling fan isn't going on when at idle. and engine temp increases. While you are driving, air is being rammed thru your radiator as you cruise along, so it isn't overheating, at idle, that isn't happening, and the fan should go on as the temp goes up. When the ac is switched on, the fan is being signaled to operate due to the heavy ac load on the cooling system.

Idle air control at base of throttle body. Passages could be plugged or idle hard stop needs adjusting.

Air Intake System Sensors Air intake system sensors include a heated resistor-type mass air flow (MAF) sensor and throttle position (TP) sensor; both supply data to the powertrain control module (PCM). The PCM also monitors engine speed.
Air Intake System Control Devices The idle air control (IAC) solenoid regulates idle speed by adjusting the amount of air allowed into the intake manifold. Adjustment is made by varying the duty cycle output by the powertrain control module (PCM). The PCM will increase the duty cycle for added mechanical or electrical loads. The IAC solenoid is combined with the fast idle control (FIC) solenoid which is turned on when the air conditioner is engaged to help compensate for the additional load. The IAC valve must be replaced as an assembly with the FIC solenoid.
Fast Idle Control (FIC) Solenoid The fast idle control (FIC) solenoid (Figure 1) compensates for idle speed change caused by the operation of the air conditioner compressor. The FIC solenoid is controlled by the FIC relay. The FIC relay is energized when the air conditioner clutch is energized and the relay allows the FIC solenoid to turn on and let an additional volume of air into the intake manifold.
Figure 1: Fast Idle Control (FIC) Solenoid

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Throttle Body (TB) The throttle body (TB) controls the amount of air that flows into the engine through a single butterfly valve. The single butterfly valve opening is determined by the accelerator pedal. The TB is cast with an air bypass channel and houses several emission-related components for the powertrain control module (PCM).
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Throttle Position Sensor (TP Sensor) The throttle position (TP) sensor responds to the accelerator pedal movement. The TP sensor is a potentiometer that transforms the throttle plate opening angle into output voltage and sends the voltage signal to the powertrain control module (PCM). In addition, the sensor detects the opening and closing speed of the throttle plate and sends the voltage signal to the PCM. Also, the TP sensor is used to determine the air intake when the mass air flow (MAF) sensor fails. This mode of operation is called Fail Safe.
The TP sensor integrates the idle (IDL) switch within the housing. The IDL switch detects when the throttle plate is closed and an idle condition occurs. The PCM is supplied with this input signal.

IDLE SPEED

well common things abt idleing is ECU....it will idle weird sometimes smioke *black* abit or choke up & die...after replacing ECU should solve the problem to idleing & air conditioner

The "Tachometer" is the gauge that indicates the engine RPM. It is not unusual for the idling RPM to drop slightly when the air conditioner comes on. The air conditioner represents a fairly large load on the engine so when it starts, the RPM will drop slightly. When driving, you'll probably not even notice that the air conditioning is a load on the engine unless you're accelerating uphill, pulling a trailer or passing another vehicle while the vehicle is fully loaded. At idle, the Envoy's computer should detect the falling RPM and make adjustments in fuel delivery to bring the RPM back up.

In any case, it shouldn't be cause for alarm, unless the air conditioner is stalling the engine. If this is the case, you are probably in need of service. The issue of low cooling from the air conditioner while idling in gear (as is the case when stopped in traffic, etc.) is correctable free of charge at the dealership on certain vehicles as a result of a recall. Your dealer can tell you if your vehicle is affected or if there is other recall work pending on your vehicle based on the VIN.

I hope this helps!