I put a new iac valve in car,,no change,,problem seems like an air leak,,have also been told that it could be the lower intake gasket is bad..when you start the car when cold,,it will run and idle perfect,,but if you let it continue to idle,,after about 1 minute,,the rpm guage goes from aroudd 1000 rpms to about 3000 rpms,,then drops to almost stalls,,then raises again to around 3000 continues to do this till car stalls..on highway,,car runs fine and doesnt stall,,but if driving in town,if your accelerating and take foot off gas,,stalls right away,,restart car and idle is over 3000rpms,,then slowly falls..but still stals,,unless you keep it running with your foot..if accelerating up hill,,and take foot off gas,,stalls immediately

if no vacuum leaks...replace the idle air control valve

lots of causes even 100 possible (under bad engine list)
bad engine, bad spark or bad fueling << in that order.
or lack of air, idle ,IAC valve stuck closed or just dirty, clean it.
bad spark," 28 year old spark parts have no chance.
clogged injectors fully or in part, x cylinders.or leaking.
bad or old bad fuel, car parked for ages? unused, is bad fuel
not told what car does good?
full engine power up hill? besides stalls how does it drive???????
check engine lamp off? driving.?
can you prevent the stall easy with a fast right foot (gas/pedal)
if yes and engine seems smooth, can be IAC bad?
or EGR sticking open makes all cars stall. at idle.
at idle EGR is not enable but if stuck open all this fails

IAC = IDLE AIR CONTROL, (VALVE)

Yes, a bad gasket would be the cause of the oil leaking out, but has nothing to do with any air getting in. There is no vacuum under the valve cover. Change the valve cover gasket and check the intake manifold and the vacuum hoses coming from it for vacuum leaks (air getting sucked in).

Check for leaking vaccum lines from the engine intake manifold. If no leak, test the IAC motor and clean out the air bypass passages per instructions below. Let me know if this doesn't solve the problem or you have any questions.

OPERATION
The Idle Air Control Bypass Air (IAC BPA) valve consists of an idle air control valve and a bypass air valve. The bypass air valve functions during cold engine conditions to increase engine idle speed. It consists of a thermowax bead and a valve.
Engine coolant is directed around the thermowax, which opens and closes the valve. During cold engine operation below 140°F (60°C), the thermowax is contracted enough to allow the valve to open. As the coolant heats, the thermowax begins to expand. When the coolant reaches temperatures above 140°F (60°C), the thermowax expands and closes the valve.
The valve controls the amount of throttle valve bypass, which ensures a smooth idle under all engine operating conditions.

1. When the engine is cold, air flows through the valve during all modes of engine operation, to maintain the factory set idle speed.

TESTING See Figures 1, 2 and 3 (if you don't have an ohmmeter, skip this test)

1. To check the Idle Air Control (IAC) valve resistance, unplug the IAC valve connector.
2. Connect a high impedance Digital Volt Ohmmeter (DVOM) to the terminals.
3. Measure the resistance.
4. The resistance should be 7.7-9.3 ohms.
5. If the resistance does not meet specification, replace the IAC BPA assembly.

Fig. Fig. 2: Connect an ohmmeter to the IAC valve; the resistance should be 7.7-9.3 ohms

At this point, if your IAC checks good, I recommend you take out the 4 screws seen above, remove the motor, and clean out the air passages/valve with carb cleaner. Also remove the big (3 inch diameter) hose from the throttle and clean out the throttle body, if dirty.

If the IAC tests bad, go to the removal and installation directions below.

The next test requires a scanner. If you don't have a scanner, skip this test.

1. To check the BPA valve function, remove the BPA valve from the engine.
2. Wait until the valve reaches room temperature. When the valve is cold, blow through the air inlet and verify that air flows freely through the valve.
3. Heat the valve with a hair dryer; the air valve should move out and block the passage.
4. If the valve does not function as specified, replace the IAC BPA assembly.
5. To test the solenoid, connect a scan tool to the Data Link Connector (DLC).
6. Turn the key ON and enter the simulation test.
7. Access the IACV Parameter Identification (PID) and turn the dial to cycle at 75 degrees.
8. Listen for the IAC solenoid to click when using the simulation test.
9. If the solenoid clicks it is working properly.

Fig. Fig. 3: Idle Air Control Bypass Air (IAC BPA) valve assembly components

REMOVAL & INSTALLATION

1. Disconnect the negative battery cable.
   CAUTION

Never open, service or drain the radiator or cooling system when hot; serious burns can occur from the steam and hot coolant. Also, when draining engine coolant, keep in mind that cats and dogs are attracted to ethylene glycol antifreeze and could drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantities. Always drain coolant into a sealable container. Coolant should be reused unless it is contaminated or is several years old.

1. Drain the coolant until it is at a level below the Idle Air Control Bypass Air (IAC BPA) valve.

The lower coolant line should be disconnected after the valve is separated from the upper intake manifold.

1. Tag and disconnect the upper coolant hose from the valve.
2. Unplug the valves electrical connector, then loosen the two nuts and two bolts attaching the valve to the upper intake manifold.
3. Pull the valve from the manifold and disconnect the lower coolant line from the valve.
4. Remove the valve and gasket from the engine.
   

To install:

1. Use a scraper to clean any old gasket material from the valve mounting surface.
2. Install a new gasket and connect the lower coolant line to the valve.
3. Install the valve and its retainers. Tighten the nuts and bolts to 71-88 inch lbs. (8-10 Nm).
4. Engage the valves electrical connection and the coolant hoses to the valve.
5. Fill the cooling system and connect the negative battery cable.

change the idle air control valve.

Idle Air Control (IAC) Valve OPERATION The Idle Air Control (IAC) valve controls the engine idle speed and dashpot functions. The valve is located on the side of the throttle body. This valve allows air, determined by the Powertrain Control Module (PCM) and controlled by a duty cycle signal, to bypass the throttle plate in order to maintain the proper idle speed. Fig. 1: Typical Idle Air Control (IAC) valve which is mounted to the throttle body - cutaway view shows air bypass direction
--- REMOVAL & INSTALLATION

1. Disconnect the negative battery cable. To remove the IAC valve, first disconnect the negative battery cable, then the IAC wire harness plug
   Next, remove the two IAC valve attaching bolts . . .
   . . . and pull the valve from the intake manifold
   
   
2. Disengage the wiring harness connector from the IAC valve.
3. Remove the two retaining screws, then remove the IAC valve and discard the old gasket. To install: When installing the valve, always discard the old gasket and install it using a new one
   
   
4. Clean the IAC valve mounting surface on the throttle body of old gasket material.
5. Using a new gasket, position the IAC valve on the throttle body. Install and tighten the retaining screws to 71-106 inch lbs. (8-12 Nm).
6. Attach the wiring harness connector to the IAC valve.
7. Connect the negative battery cable.

High idle
Changed IAC still the same, shown on scanner IAC 50-60 %, if it set to 40% the Idle is ok. What cause the PCM to set IAC too high? Is any one know?

What size engine 2.4 or 3.4 L ? Dirty throttle plate , fuel injector's need cleaning , EGR valve sticking open a little , intake manifold leaking , IAC - idle air control valve passage carboned up .
Idle Air Control Valve
007 Idle Speed Problems Scan Data for Idle

While looking at the engine from in front of the car with the hood up..
Locate the TBI assembly ( follow the air intake tub from the cor support back. It leads directly to it ). Next look on the lower left side of the TBI just above the throttle linkage connection to the TBI.
you will see what looks like a little molded bullet sticking off the side with a screw sticking out of it making contact with the linkage assembly. On the back side of that little bullet you will see a torques head type screw head. adjust that forwards to increase idle speed or back it off to lower idle.
If you have a high idle condition the chances are it is not due to the idle set screw. Its more then likely either deteriorated vacum lines, deteriorated TBI gasket or a bad Air Idle Control Motor ( IAC ).
If you adjust the screw and nothing happens worth noting then check the vacum lines and replace. If nothing happens still then change the TBI gasket where it mounts to the intake.
If that doesnt do it then your left with the more costly option of changin out the IAC for a new one. They run from $75 - $125 depending on where you shop.
If after you change the IAC and it is still acting out then you may have an intak emanifold leak, or a head leak.

It is the head gasket. Have that replaced and you will be fine. You have an air leak. I was told by the mechanic at mazda that the anti freeze eats away at the gaskets. CRAZY, but it works. I still have an issue with my 2001 Tribute revving while in park. Its always something.

You may have a vacuum leak at the intake. Spray some WD-40 along the intake while it's running. If the car's idle changes you have a vacuum leak there. Replace the intake gasket. Your IAC valve (Idle Air Control valve) could be acting up as well.