What causes sputtering in the engine of a dodge neon, does it need a tune-up, cause I keep up on the engine maintenance?

Nikki is the engine light on, are there any codes,have you had a tune up or any other work done lately.when you say it won't start when warm(do you mean engine will not turn over, or does engine turn and refuses to fire.
If I had to guess failing fuel pump, they tend not to build fuel pressure when ran a while(warmed up) and when left to cool build somewhat better pressure.
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Is Your Fuel Pump Going Bad
How do know if its fuel filter or fuel pump that is causing the problem
How To Diagnose Fuel Pump Failure EricTheCarGuy
http://www.clarks-garage.com/shop-manual/ts-01.htm#hot-start

While your car is running.......pop the hood and find the throttle body. The throttle body is where your air filter tube/hose goes to the engine. Locate the throttle position sensor which should be on the side of the metal throttle body. This should be the item causing this. If you grab the plug that is on the sensor and wiggle it while the car is running then the engine should rev and act up if thats the problem. If not let me know and I can direct you further. Thanks.

most likely need a tune up.or lose wire

u may have a sensor or computer issue--it shud be scanned--the fuel injector pump is the heart of a diesel-probly needs a tune, rebuild or new one--pick up a haynes manual for maintenance details or go chilton online

WHEN A/C IS TURNED ON IT PUTS A LOAD ON ENGINE. U MAY WANT TO DO A TUNE UP AND MAKE SURE THAT THERE ARENT ANY VACUUM LEAKS. ALSO MAKE SURE THAT THE COMPRESSOR IS NOT GOING BAD. THAT WILL CAUSE EXTRA AMPERAGE ON SYSTEM

It's really hard to give a specific cause for something like this with out more information. If for instance it is a miss-firing cylinder, there are several possible causes for it ranging from a bad spark plug, bad 02 sensor or even a burnt valve. However there are a few items you can check and maintenance the can be preformed that may help out. At the very least it will eliminate them as a possible cause.

The most common cause of rough idle is worn out components. These include air cleaner, spark plugs, wires, cap and rotor. These are all items that should be replace at the time of a tune-up. If it hasn't had a tune in a while, that is a good place to start. This will also give you a chance to inspect the spark plugs. The condition and color of the electrode at the bottom end of the plug will give you a good indication as to how well the engine is performing. The first link I provided below will give you a way to compare what your plugs look like and what would cause that condition. Included with the items for a general tune-up, A good fuel injector cleaner should be added to a couple tanks of gas as well as a injector cleaner that runs through the intake manifold.
During the tune-up you should inspect all the vacuum lines and listen for any leaks while the car is running.

Before doing anything that's unnecessary it's a good idea to check the error codes. You do this by turning the ignition key on-off-on-off-on within five seconds. Only turn the key to the on position not the start position. If your odometer is digital the codes will be displayed there. Examples are P0303 and P1283. If your odometer is mechanical the codes will be displayed in a series of flashes, a pause and more flashes from the engine light. To be honest it's much easier to take the car to someplace like Auto Zone where they will read error codes for free then dealing with the flashing pause system. After you have the code (if any), you can check them at the second link I added below. Make sure to check both the Dodge specific codes and the generic codes.
These codes help by giving you specific information on any system that is not functioning properly.
Once you have recovered the engine diagnostic codes if any or you are at all unsure of any part of this solution please re-post.
Hope this helps.

http://www.engine-light-help.com/dodge-check-engine-light.html
http://website.lineone.net/~srbrock/01a.jpg

It can cause sputtering but it wouldn't really cause the plugs to foul. Try pulling the plugs and getting a good look at the electrodes and you can get a good idea of why they're fouling by looking at them. Here's a good guide with some pictures to help you:

http://www.gnttype.org/techarea/engine/plugs.html

Just to let you all know it ended up being the CENSOR in the trany that was bad.

the cam sensor definitly can cause the problem. pull the trouble code and make sure the check engine light is for the cam sensor. if so, replace it and retest

Have you had the fuel pressure checked? Fuel filter changed?