When i start her up, she runs for a few seconds then shuts right off. But if i keep a throttle to her she'll stay on. And as soon as i lay off the throttle it putts around and shuts off. I have to keep the throttle down for a little bit before i take it off, then she runs fine. What would cause this?
BTW, this is a 1996 5.0L Bronco

 

Oh and BTW, it start to do this till it started to get cold out. When i drive it and park it for like an hour, it doesnt have that problem anymore. But if i let it sit over night, ill have that problem again.

 

And...sorry.....I forgot to mention, its not an instant shut off. It rough idles and spits and sputters. Then shuts off

 

My Mustang did the same thing as you're describing. The AIS motor was sticking. (they get dirty) Check for codes.

 

How do you clean them? And why would it only do it when it got cold out? When the engine is warm, its starts right up.

 

Dirty IAC passages. Coking in the throttle body and IAC valve will cause this kind of issue. Cleaning can be done with any carb cleaner that is safe for "SEALED throttle bodies". This is critical or you will strip the sealer off the walls of the TB leaving it porous and ready to absorb all kinds of crud that shouldn't be in it. Most stuff is catalytic converter safe these days but any cleaner you use should be "safe for catalytic converters" as well. The IAC is held to the side of the throttle body with two bolts. Take care NOT to get liquid cleaners or water into the solenoid (electronic) portion of the assembly. You will most likely need to replace the gasket between the IAC and the TB when you do this.

What is happening: During the cold start, the ECM tries to dump more fuel into the mix which of course is necessary. The problem arises when there is too little air in the mix to begin with (caused by clogged/dirty IAC valve) and when the O2 sensor "thinks" the mix is too rich, the ECM responds by dialing the fuel back... the result; too little air AND too little fuel to keep the truck running before it warms up. This is why you can get around the problem by opening the throttle just a bit.

You might want to warm the truck up to normal operating temp and then disconnect the IAC solenoid at the connector while the engine is idling. The truck should do the same thing it is doing in the cold IF the IAC solenoid is working properly. In other words it should wind down, sputter and die shortly after disconnecting the IAC connector. If it does, then the IAC solenoid is working properly. If it doesn't you have worse problems. Again, make sure the truck is at full op. temp. before attempting this test. Make certain to clear fault Codes after performing this test as disconnecting the IAC electronics will throw a fault Code.

 

Sorry, I guess I could have elaborated a little better but greystreak nailed it! There is a foaming throttle body cleaner that works pretty good. The better cleaners have a tube where you can get into the small passages better. Just MAKE SURE they say for throttle bodies only!! Using the wrong cleaner can damage your throttle body or other components!! And if I can channel my wife who is in the eye care buisness.........WEAR EYE PROTECTION!!! That stuff will burn the crap out of your eyes!!!