Hi, it's not so much air intake as it is air/fuel ratio. If the air coming in is properly measured by the MAF sensor and the injector pulse is thereby adjusted by the computer to provide the appropriate air/fuel ratio, the engine will have power to idle. If air is getting in from a vacuum leak or thru the EGR valve unaccounted for, the mixture will be too lean to maintain the spec idle. By increasing the load, such as when you turn on the A/C, the computer compensates by allowing more metered air thru the throttle/idle air control valve. Since this airflow has come thru the MAF sensor, the injector pulse will be increased to compensate.
So the extra information you have given tells us you likely have a vacuum leak of an EGR or purge valve that is stuck open.
Vacuum leaks cause the engine to run lean and draw too much air
for an idle setting of the throttle. An engine that will not idle due to a vacuum leak
generally has a pretty good leak that you can often hear by walking
around the engine. Check the big hoses first, like the one to the brake
booster. Then check every other hose connected to the engine intake
manifold. Check both ends of every hose for a poor connection and repair
or replace any leaking hoses. Although rare, a leaky intake manifold
gasket can also cause an engine to stall, but usually a leaky gasket
will set a trouble code P0171 and/or P0174. To check for leaky gaskets,
start the car and spray carb cleaner at the intake manifold gaskets. If
the engine revs, you have a leak. If you have an upper as well as a
lower intake manifold, check both sets of gaskets.
EGR Valve: The exhaust gas recirculation system is required by
many engines to meet national or California emission standards. When the
computer deems the conditions appropriate, it opens the EGR valve and
controls the flow of exhaust gas back into the intake manifold to
provide inert mass that absorbs the heat of combustion, thereby reducing
NOx products. There are many variations of EGR systems, and the valves
may be controlled by vacuum, electric motor, or electric solenoid. Many
systems include a sensor to feedback either flow or valve position to
the computer. Most computers do not open or extremely limit the EGR
valve opening during idle because of the difficulty in controlling idle
mixture. The default position of the valve is closed. However, if the
valve has not closed properly from off-idle operation, the EGR flow can
cause a rough or poor idle. If necessary, use a manual for your vehicle
to obtain a procedure for removing, cleaning and testing your EGR valve.
At a minimum, make sure the valve is able to close with no control
forces applied. The valve is
usually mounted in the intake manifold and exhaust gasses are either
routed through the heads to the intake manifold exhaust passage or they
are piped to the valve from the exhaust manifold.
2 liter engine EGR valve
5.
EVAP Purge Valve:
The evaporative emission system is designed to limit the release of
fuel vapors from the fuel tank. Up to a certain design pressure, vapors
are stored in a charcoal canister and are later drawn into the engine
to be burned. The computer determines when conditions are appropriate
for vapors to be allowed into the engine and opens the purge valve with
precise solenoid pulses. As with the EGR valve, the computer stops or
severely limits the flow during idle. However, the valve may become
stuck, inoperative, or clogged with charcoal bits (if the canister is
leaking it's charcoal). This valve may be difficult to find, though it
is usually mounted on the intake manifold, throttle body, along the air
inlet hose or on the charcoal canister itself. If you aren't sure you
have found it, trace the hose back to find the canister. Remove the
valve, clean it with carb cleaner, and check that it closes on it's own.
If you have a manual that provides tests for the valve, run the tests
to verify proper operation.
2 liter engine purge valve--usually mounted on firewall:
