Idle Problems

[RxPx33]

I'm not savoy with mechanical things but I bought this truck to teach myself what i could as I went along fixing it up. So anyway here is my problem maybe someone could shine some light on whats going on.

I have a 1970 C20 with a stock 307.

I changed the oil yesterday and since I live in Pa and its getting into the colder months I used 10w-30. I couldn't get the oil filter off so I just left it on there till I can get a tool to take it off. Also while the oil was draining I decided to take off the air filter holder and sand some of the surface rust off and give it a little black spray to put some color back on it. After it dried I connected everything the way it came off and finished with the oil change.

Now here is the problem the Truck before all this ran great and idled really good. On Cold start i just had to feather the gas like 3 or 4 times and the engine would stay at a decent idle till I was ready to drive. Now when I start it i have to continuously feather the gas to keep it from stalling out. I sat there for 10 mins yesterday, to see at what point it would idle on its own without stalling and it never happened. When I let go of the gas it just stalls out. So I decided to take it for a drive (now having a 4 speed and not being able to idle in my little town of low speed limits and tons of stop signs was a blast trying to keep the truck from stalling), after i got it on the highway and drove about 10 mins down the road at about 45-50 i pulled over. It finally idled on its own but very low and sounded like it wanted to stall but it didn't.

So any help here would be great.

Also should note that the oil pressure gauge drops all the way down when I don't press the gas. I know you cant trust the gauges on these trucks and honestly i never paid attention to it when the truck was running good so not sure if it did it before this or not.