Rough idle in park

It could be a damaged or still dirty fuel injector(s). A damaged\dirty fuel injector will not only causes issues with driving, but the effects will persist even as the engine idles. Instead of a smooth engine idle, it will be rough and irregular when the fuel supply is abrupt. But I do agree with Steve. Most part stores can run a diagnostic test to determine what the problem is in general.

I think you are on the right track with a tune up. Replace the wires, air filter and oil as well. I also would run a cleaner through the fuel lines. An STP or a Lucas would be better.

Change oil thicker weight with some Lucas and injector cleaner in gas trust me

I WOULD SAY YES BECAUSE THE LUCAS FUEL INJECTOR CLEANER IS JUST HELPING THE INJECTOR SPRAY BETTER

It could be something as small Such as plugged fuel Injectors. Run a bottle of fuel injector cleaner (I use Lucas Fuel Treatment) Through the system and fill your tank with a higher grade gas and it should improve...

I’m happy to assist further over the phone at https://www.6ya.com/expert/cameron_6665f74c5d46fc23

seeing how the truck is an 88 there could be a few solutions that will not cost alot of money. I would try to add fuel injectior cleaner to your next full tank of gas as well has using a higher octane fuel or octane booster. Also try some heet. this takes some of the extra moisture out of the gas and should be added in a full tank as well. Some of the Lucas brand injector cleaner will remove moisture. If there is any knocking in the motor, on your next oil change put in a bottle of Lucas oil treatment or something I use called Hyper-Lube. They both are only 1 quart bottles so you will short the amout of oil put in the engine by 1 quart. When the truck is sitting overnight or for a few hours especially in a cool environment the oil will get thick, when the truck warms up the oil thins and you notice problems like what you described. I live in Indiana and the winter here can be a bit rough on a car/truck. If additives don't solve the problem then you will have to look into the possibility that there is a mechanical/electrical component that is bad. They can be:
throttle position sensor
dead fuel injector
lose of compression in a cylinder
dirty fuel filter
dirty air filter
spark plugs
engine timing off
faulty spark plug wire/ wire being on the wrong plug causing firing order being wrong
since it runs fine at driving speed I would check into the fuel injector cleaner 1st. The injector or the throttle position sensor.
I have a family member who has the same truck and for a smaller truck it's pretty tough. Definately a keeper

You can use any of the following weights of motor oil: 5W30, 10W30, or 10W40. Personally, I use Mobil1 Synthetic 5W30 in my pickup. Synthetic is better for your motor (you can go 5,000 miles between oil changes with synthetic oils) but once you start using it it's better if you stay with it meaning every oil change you use synthetic oil.

well its always recommended every 3000 miles to change the oil if you are using mobil1 full synthetic oil then every 5000 miles transmission i recommend every 45000 miles 60000 mile should be radiator fluid,power steering,fuel filter if trans hasnt been done then transmission

The Impala takes an oil viscosity of 5W-30 or 10W-30, with 5W being the preferred. With this age engine you might want to switch to a synthetic oil, but once you do, stay with it.

Once you have the new PCV valve locate the old one on your engine. It will sit on the middle of one of your valve covers (most likely passenger side) and will have a line that connects to the top of the valve. Simply pull the old one out and put the new one in snapping that line on the new one. Should only take about a minute to do. Hope this helps, let me know if it does.