When i turn on my a/c the idle speed lowers until engine turns off.

Press primer until fuel fills bulb and flows out carburetor. If no fuel in primer bulb then check connections.

Check fuel line connections by disconnecting retun line to tank (without filter) and pressing primer bulb. Fuel should draw from tank (filter), into bulb, out bulb to carb and expel out carburetor. If not the bad lines, filter, or lines not connected correctly.

With fuel primed, turn both high and low speed needles in (CW) until seated, do not tighten. Then turn needles out 1 1/2 turns for initial settings. These settings are only to get unit running. Increase idle speed setting if engine stalls. Adjust low speed, then high speed and lower idle speed back to normal.

I am assuming a carburetor is used. That said, locate the fast idle adjustment screw and turn it counter clockwise until RPMs get to the desired speed. If you have EFI , I can't help

are you asking how do you set the idle mixture. if so all you do is locate the idle mixture screws at the front of the carb at the base. there is one screw for each venture. turn in(one at a time) screw until it bottoms then turn it out 3-4 turns with the engine off then do the other screw. start engine and then turn each screw(one at a time) in until idle starts to run rough then back out, until you get a smooth idle speed then do the same to the other screw. then if you need to check idle speed with a tach and set it to 750 rpms. if you mean rebuild the carb kit comes with instructions and pictures, you can take photos while disassembly to show/remind you where the components go and pay particular attention to the jets and metering rods.

Chech idle adjustment screw, and spark plug gap.

Check the idle air control motor on the throttle body to see if it is adjusting the lower end throttle speed by rotating the throttle plate open a bit when the a/c or heater is turned on at idle.

Do you have any codes stored in the computer regarding this malfunction?

Check idle speed and mixture at idle. Often with too fast idle speed, engine will not shut off. Many vehicles had an electric solenoind that released the idle speed to much lower, at key off.

The problem is in the idle air control motor. It is mounted on the throttle body with two bolts, you can pull it off and make sure it is not caked with carbon also check where it mounts on the throttle body and make sure it is not caked with carbon.

idle stepper motor(IAC) controls idle speed it is located on throttle body
IDLE LEARN PROCEDURE
Whenever the battery cables, the electronic control
module (ECM), or the ECM fuse is disconnected or replaced,
the following idle learn procedure must be performed:
1. Turn the ignition ON for 5 seconds.
2. Turn the ignition OFF for 5 seconds.
3. Turn the ignition ON for 5 seconds.
4. Start the engine in P/N (park/neutral).
5. Allow the engine run until the engine coolant is
above 85_C (185_F).
6. Turn the air conditioning (A/C) ON for 10 seconds, if
equipped.
7. Turn the A/C OFF for 10 seconds, if equipped.
8. If the vehicle is equipped with an automatic transaxle,
apply the parking brake. While pressing the
brake pedal, place the transaxle in drive (D).
9. Turn the A/C ON for 10 seconds, if equipped.
10. Turn the A/C OFF for 10 seconds, if equipped.
11. Turn the ignition OFF. The idle learn procedure is
complete.

Before you start check the status of your choke. One that is stuck on will cause a high idle. If the choke checks out, proceed to the following:


You should have what's called a 2 needle carburetor. A larger screw adjustment for idle, and a smaller for high speed.

Start by adjusting your low speed (idle) needle until you reach the desired idle. I prefer about 850rpms. Do this with the engine running and adequately warmed so that your adjustments are not thrown off by the automatic choke.

Next slowly open up the high speed needle. As you open it your idle speed will gradually increase. Adust it in 1/8 turn increments, pausing after each adjustment to allow the changes to take affect. Keep opening it until you stop increasing your rpms, then take it back 1/8 of a turn.

Next readjust your idle mixture screw so that your idle is back down to 850rpms.

Hi jmach,

There is nothing wrong with your vehicle and no need to have anything repaired.... The high idle speed is controlled by the on board ECU...(the Electronic Control Unit).... When starting the vehicle from cold, the automatic enrichment of fuel increases the idle speed... Depending on the ambient air temperature.... the colder the weather, the longer the engine will take longer to return to normal idle speed. Thats how it's designed to operate.

Regards Johngee10