Why is my 91 talon idling erratically? I have replaced the idle air control, mass air flow meter, tbhermostat, radiator, clutch, cleaned throttle body, and still idles up and down. The car run s beautifully when it's in gear. I even passed emissions. Please help.

Possible vacuum leak. Check all hoses under hood for cracks/disconnections/leaks. Will be heard by a hiss type noise. You may have to scan computer to monitor sensor operating parameters with a scan tool to isolate this problem

Sir, your question is not very clear, but I will still try to post a solution here. Engine missing could be due to any problem in fuel system, ignition system, engine or ECM as well.

LOW ENGINE IDLE SPEED (Poor idling):
-Throttle body (do the cleaning and idle speed learning)
-A /C signal circuit
-Fuel pump control circuit
-Fuel pump
-Intake system
-P C V valve (clogged or open) and hose

ROUGH IDLING:
-Cylinder Compression
-Ignition system (Igniters, spark plugs, wiring harness)
-Spark plug fouled, gap too wide or too short. (1.00-1.1 mm)
-Fuel injector circuit
-E C M power source circuit
-Fuel pump control circuit
-Fuel pump (required pressure 44 psi - 49 psi)
-Throttle body (cleaning)
-Intake system
-P C V valve and hose
-Air fuel ratio sensor
-Heated oxygen s ens or
-Mass air flow meter
-Idle hunting
-Throttle body
-Intake system
-P C V valve and hose
-Air fuel ratio sensor
-Mass air flow meter

HESITATION/ POOR ACCELERATION:
-Fuel pump control circuit
-Fuel pump
-Spark plug
-Ignition system
-Fuel injector circuit
-E C M power source circuit
-Mass air flow meter
-Throttle body (do cleaning)
-Intake system
-Valve timing
-Cylinder Compression

(1) clean the throttle assembly. They are very sensitive to build up also and they are very cheap change out the throttle body sensor. The TBS allows are to by pass both of these will cause erratic ideal. The mass air flow will not cause erratic idle but your car will be very loud and run rough. Failing this (cheap fix) I would suggest to look at the ignition coils.

Have you checked the TPS throttle position sensor?

Yes a vacuum leak could be the problem. Try filling a spray-bottle with tap water and spraying the vacuum lines and connections while the car is running.

If it idles up and down real high, its the throttle body sensor. If it's a low up and down idle and runs rough it is mass air flow meter. If you unplug the mass airflow meter and it will just low idle (no up & down) then the mass air flow meter is bad.

couple of possible problems

first thing i would check is to make sure air intake hose between Mass air flow sensor and intake doesn't have any cracks holes make sure clamps are tight

secondly check for vacuum leaks carb cleaner works great for this spray around intake gaskets throttle body fuel injectors vacuum lines when spraying u notice change in idle (if idle picks up or stubles) that where your problem is example you spray around intake gasket and idle picks up you have bad intake gasket

third thing is to try and clean the mass air flow sensor they make special cleaner for this (u can use carb cleaner for this but it can leave residue on sensor and damage it so it not recomended)

my best guess for you with all three o codes is you have a vacuum leak somewhere

according to your information it's faulty mass air flow sensor, check mass air flow sensor first, when the Idle rough just disconnect the air flow sensor wiring socket if it's better than when it's connected it's faulty air flow sensor, mass air flow sensor have fitted between air cleaner housing and throttle body, you can see wiring connector been connect on it you have to turn it anticlockwise and remove it. when you fix it back do the reverse order, if it's faulty replace air flow sensor. is this information helped you?

3 possible problems your mass are flow meter/senso could be going bad but not bad enough to register a fault, the same for your idle air valve and also your throttle position sensor. all 3 of these are on your throttle body .
with the engine running tap the side of the mass air flow with the back of a screw driver, if the engine sputers mass air flow needs replaced.you can try cleaning it with some mass air flow cleaner if you cant find that at your auto parts store get some electrical parts wash. your idle air valve needs to be cleaned or replaced there hard to get off. your throttle position sensor , you need to know the setting ,if the auto parts store cant give you aprint out of instuctions best to let a kia dealership do it and pay out the ****.

The idle air valve (located below the throttle body) provides the control for constant idle speed. In order to set the correct air valve opening to achieve constant idle speed, the fuel injection control unit uses information from the air mass meter, throttle valve switch and the ignition control unit (RPM signal) to regulate the output current to the idle air valve. This means that the idle valve is not affected by air leaks or a jammed throttle valve.