What causes an fuel injection engine to run OK when cold but then splutter at low revs when warm?
You might have a faulty oxygen sensor. Typically, when cold, the engine management system operates in "open loop" mode ignoring feedback from oxygen sensors because they don't work properly until they heat up to a specific temperature range. Once the sensors heat up, the computer goes into "closed loop" mode using the signal from the oxygen sensors to help adjust the air/fuel mixture. If one or more sensors are faulty, the fuel mixture may be incorrect and cause a poor running condition.
Another possibility is that you have a running problem which is noticeable when the engine is turning slowly. Air metering, EGR system, and mechanical engine problems are your most likely suspects here. When the engine is cold, the computer raises the idle speed of the engine to warm it up faster and to prevent stalling which masks the problem until warmup occurs.
== == -you might also have a bad distributer or a bad catalytic converter or muffler