1998 Lumina 3.1, idles well when cold, missing and stalling when warm or accelerating. Changed coil packs and spark plugs

Sounds like you have a vacuum leak and when you accelerate it's sacking to much air the egr valve can cause this also

With the car running take a can of starting fluid and spray around the intake. those cars are known for bad intake gasket leaks. if the engine idles up on its own when you spray it. you have a bad intake. make sure to check and spray vac lines as well.

Does it use spark plug wires or individual ignition coils for the each plug?. My 98 intrepid uses coils and occasionally I have to change them out cause it would start to miss when normal temperature was achieved. If it uses wires, try replacing them, along with the spark plugs.

could bea few things. Excessive moisure, low fuel pressure, Faulty coil pack, spark plugs gap or wires. Have you changed any of those at all? Let me know

it sounds like you need to inspect your spark plug wires and spark plugs. if they are ok it could be your coil

have you tried testing your ignition coils, there's 3 of them in a pack, i've had to change a couple when my lumina euro was running badly.
the coils send the spark to the spark plugs, if you have a bad coil, the cylinder won't fire. which would explain the gasie smell. a bad coil will also contribute to loss of acceleration, power and a rough idle.
the coil are rather cheap, about $20cdn each. usually one is dead and the others are good.
to test if your coils are working, what you can do is...
- start your car - unplug one cable and replace it and listen for a change in sound in the engine. if there is a noticable change in sound then that cylinder is working. - if you unplug a cable and nothing happens, and plug it back in and nothing happens, that coil is dead. you will have to replace it (one coil powers two cylinders, each independantly. one cylinder on a coil may work while the other is dead).
*please remember to unplug and replace a cable one at a time. and while doing this don't touch the metal framing of your car, our you'll get a nice zapp.
this is a cheap and easy way to test you coil pack. my friend spent about $1000 and 3 mechanics and they never checked the coils. i did, and didn't cost him a thing.

Did you put plug wires on it? Also these are good for having injector problems.

the idle controls could be the problem

Im having the same issue I believe. I have a 94\' Chevy 1500 and when i accelerate it will jerk like the gas has cut out but it wont stall. It just jerks and slows me down. It only seems to do it when going up a hill. I feel like it could be the fuel pump or possibly some intake gaskets?

check the crank sensor