Replaced water pump and timing belt on my '95 Plymouth Neon with 154,000 miles. Starts right up (warm or cold) but has a very lumpy idle and dies when I stop at a traffic light. It starts right away after it quits and drives normally with power at all speeds.

water pump not properly installed
take it back for warranty rework

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.
press the helpful button

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

The timing belt could have been loose, or the tensioner not set correctly. It sounds as if your timing belt has slipped.

I notice that you replaced the water pump,Did the car over heat at any time, If it did end you didn,t stop right away when it first happen, It can do real serious damage to the engine, That will give the syptons you are describeing,If you notice that the car starts to use more oil, That is a deffenet sign there was damage done to the engine,That it done damage to the piston rings, Have you changed the thermostat in it? It tell me allso when you stay your temp gauge is not working that the termostat .Might not be functioning(Properly)
End mess up the temp (Sending) unit. If the car is over heating there will be a loss in power,

the valves will also be bent. Its probably not worth it. thats why it should be replaced every 90K miles with a water pump and tensioner.

better have a shop check it out. If you have approx 90k miles on that car and the timing belt has not been replaced, replace it ASAP. if it breaks, the valves will be bent and th ecar will not be worth fixing. if it has been replaced before, then replace it at another 90k be sure to replace the water pump and tensioner at every timing belt replacement.

Did you replaced your whole distributor or just the cap and the rotor? Have you check the pressure on you fuel line it could be your fuel pump.

there are several.4-6 or more?? if the coolant is rusty, plan on doing all of them or sell the car. BIG $$$$...If you have not kept up with the coolant service,you will have much bigger problems later on. how many miles? at 90k miles replace the timing belt, tensioner and water pump, use factory chrysler parts only. if you dont and the belt breaks, or water pump siezes, the engine will be trashed.

I had a similier issue when I bought a used 95 Neon. Check your spark plug cables for worn surfaces. They like to rub the hood and the valve cover. When they wear down and heat up they discharge to the hood and v/c. This creates low voltage condition that causes the car to nearly die.

You have the timing belt off. If the engine computer sees the Crank sensor and the cam sensor don't line up, the engine computer will shut down two injectors. It sounds stupid, but trust me. I have seen this before.