Car will not start without pressing gas pedal to keep idle speed up. If I keep idle at 900 RPM or higher it runs as long as foot is on gas pedal. It then stalls out when I take foot off gas pedal. No problems prior to this.

Hi Wendi:
If the engine runs fine except when you don't have your foot on the gas, maybe the idle stop needs to be adjusted. With the engine off, have someone step on the gas pedal while you look at the linkage at the carb. There should be a plate with a screw in it that keeps the butterfly valve from closing completely. This can be adjusted with the engine running. (SAFETY FIRST - MOVING PARTS CAN BITE)
If the engine will only run at not nice too high RPM, chances are that the idle jet in the carb is plugged, and a carb cleaning and possibly overhaul may be needed.

It,s either not getting enough gas or not enough air. Check has and air filters.

If you can keep giving it gas and it runs above idle with no problem, then you have a blocked or bad idle control valve on the throttle body assembly. With your foot off the gas pedal, the large throttle plate inside the throttle assembly is closed, but some air is let in through the idle control valve or motor through a separate passage. This can get clogged with deposits over time and poor idle results. The valve is controlled by the engine computer. It is how the computer controls idle speed- more air if the idle control valve is opened wider, higher idle speed.

"...like its not getting any gas..." Oh yeah, it's getting gas, the injectors are still pumping gas into the cylinders, but it may not be getting any air. All the accelerator pedal does is control the air supply into the engine through the throttle body. So modern cars have an air pedal, not a gas pedal. Then the computer takes over and matches the correct amount of gas through the injectors to the known supply of air in the intake manifold. Neat system, eh? Sorry if I sound so pedantic, dale. check your idle control valve.

Should be on or near the fuel injector supply rail.

idle speed control or a vaccum leak

This can be pretty easy to fix. Spray the engine seams on the intake manifold with water from a spray bottle while the engine is running. If you have a manifold leak, the engine RPM will drop or the engine will stall when you find the air leak.

Think of this as having the throttle open. When you press down on the throttle, you give the engine more gas and more air. An air leak on the motor will also let it speed up without your foot being on the gas pedal.

If you find no leaks, check the fuel pressure. There can be a fuel pressure regulator problem if it no longer restricts the flow of fuel.

Another part called a throttle position sensor can cause problems if it is shorted and fails to regulate the throttle.

I believe you should just set the idle higher at the throttle body or MAF so it gets enough air and fuel to keep running. Those butterflies have to be cracked open a little to start with so it's getting enough air to run without you having to keep your foot on the throttle pedal.

For this problem, i suggest you to go through this help links.Click the link below to go through the troubleshooting procedure :----Car Idles rough and quits when gas pedal is pressed less? http://technoanswers.blogspot.in/2012/01/1999-ford-f-150-idles-rough-and-quits.html-----------Car only starts when gas pedal is pressed? http://technoanswers.blogspot.com/2012/01/car-only-starts-when-gas-pedal-is.html
-----------Car won't start without hitting the gas pedal? http://schematicsdiagram.blogspot.com/2011/12/car-wont-start-without-hitting-gas.html
---------Car dies when gas pedal is pressed? http://schematicsdiagram.blogspot.com/2011/12/car-dies-when-gas-pedal-is-pressed.html
------------Pushing on the gas pedal, but the car slows down? Gas pedal to the floor and the car slows down? http://technoanswers.blogspot.in/2012/02/pushing-on-gas-pedal-but-car-slows-down.html
-----------This will help.Thanks.

Could be several things.. I would suggest replace the neutral safety switch, all O2 sensors and fuel and air filters, PVC valve and if needed plugs n wires..
The issue could also be a bad throttle body.. Should be a good idea to get it hooked up to a diagnostic machine - get the codes and then you will know more of what you are dealing with..

Have a great day !!

idle air speed control valve(iac),too low idle or driveline problem like play in the drive shafts. if you put it in park and give it to say2500 rpm and let go of the throttle,does it return to 900rpm?if it dips down to 5 or 600 then to 900 the iac is bad.