Zao's answer is also a good one. Assuming the engine is carbureted then his answer would be spot on. OLDER cars have a fuel injector (EFI systems) that sprays extra fuel into the intake manifold plennum. There the richer gas to air mixture helps run the engine during idle.
The causes of your problem can also trace out to an O2 sensor that is faulty. The ECU (Engine Control Unit (computer)) may be thinking the exhaust air stream is too rich and is leaning out the engine. During cold starts a lean fuel / air mixture will usually stall the engine. Your problem might be the MAF sensor (Mass Air Flow). It's ability to sense low air flow may be diminished and the ECU can't get a good read on engine performance. OR it could be a bad thermal sensor and the ECU thinks the engine is up to temperature and supplying fuel for a warm engine.
To say exactly what is the problem will require further diagnostics. While I appreciate Zao's answer, it makes some assumptions that at this point can only be reasonable for a single circumstance. Other factors need to be accounted for. Even vacuum leaks such as a crack in the intake manifold can act like this. When the materials are cold they contract, allowing more cold and unmetered air into the engine, thus leaning out the fuel air ratio. When the materials warm up they expand enough to close the leak, at the same time a warmer engine runs better, and you don't notice any problems.
The ECU should be throwing a code. Is your CEL on? (Check Engine Light) If so it's telling you there's a problem. Go to Auto Zone and have the code read for free (or any other major auto parts store) and find out. If the CEL is not on when running the engine then shut the engine off for five minutes. Start it again and watch to see the CEL comes on for a few seconds. All cars will light all the warning lights on the dash as a way for you to tell if you have a burned out bulb. If the CEL never comes on then you may have a burned out bulb, and the computer has no way of warning you of any problems.
Yeah, there's a lot more to consider these days when it comes to car engines. You can't just say "This is the problem" without knowing all the possible parameters. But you'll figure it out now. I hope.
Hope this helps.
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The electronic choke is not engaging properly, if at all. The choke allows a cold engine start, without raising the RPM's much. Your foot on the gas "warming it up" is giving it the same amount of fuel, just less air.. The choke is letting in less air (choking the air supply), enriching the fuel. This lets it run steady and warm up without raising the RPM. Which on a cold day, or any day for that matter, if rpm's go high before the oil has time to circulate fully (right at startup), it can cause premature wear on engine internals until they get a fresh dose of oil. Just my two cents. Have fun and be safe :)
Look into an "idle air control valve" replacement. It may not be closing all the way, if at all. Sometimes you can get away with just cleaning it.
The temperature sensor that the ECU uses to adjust the mixture for cold starts and idle may be bad causing the computer to think the engine is already at operating temperature. Get a cheap scan tool with a real-time display feature so that you can see what the computer is seeing.
Remove and clean the idle air control valve. Replace the idle speed sensor. Both of these parts are screwed into the front of the throttle body.
2003 Chevrolet express 3500 6.0L V8, does not idle in the morning after starting. I have to press the gas for a minute then it will idle/drive run with no issues. Once the engine is warmed up the van will start normally and no issues as well. Only happens once the van has sat for 8+ hours. Any ideas?
