80 Century with idle issues

I've got an 80 Buick century with a 3.8 liter engine and 2 barrel carb. Here is the issue....

The engine runs rough when I'm stopped in drive at like a stop light for instance. It doesn't die, but sounds like its going to. I've tried everything I can think of.... New choke pull-offs, new plugs, wires, cap and rotor. I have cold stall issues when I try and start it in the morning and it runs really rough in drive when I give it gas for the first few mins until it warms up. In other words if while its warming up I give it too much gas in drive I feel it loosing power and too little gas wont get me moving. Once its warm it runs fine, but it still runs rough when stopped in drive. It seems to run rougher when stopped in drive once the engine fully warms up.

Could it be a vaccum issue? I've inspected most of the hoses and they all seem to be intact and in good condition. I should also say that it smells like its running really rich.

WHAT COULD IT BE?

This actually sounds like a sticking choke. If it is running poorly when it is cold it may not be closing properly and if it runs bad when it is hot it may be sticking partially closed but since it runs fine when hot I suspect the choke is not closing properly. A choke can be a really hard thing to work out sometimes. I would also check to make sure that all the vacuum lines are good. You said you have checked most of them but if you haven't replaced them do it as they are 30 years old. You may need to replace the entire choke assembly. It would probably be easier to try another carb.

Because it is a carb. it may also have a float that is sticking causing it to put too much fuel into the engine and therefore run rich but I doubt that this is the case.

Okay, let me give you a run-down of my typical experience with it each day just to make sure I'm not confusing. I'm dealing with 2 problems....

So I'll go out at say 9am to start it for the first time in the morning. I step on the gas pedal one time to prime the engine (otherwise it wont start) and turn it over. It will start up nice and clean and almost immediately die. I can kind of step on the gas pedal gently to try and keep it running, but if I depress the pedal too much it will die. So after it dies I'll pump the gas pedal one more time and turn it over and it usually fires up and stays running long enough for me to play with the pedal and find the sweet spot to keep it somewhat accelerated. If I give it about 3 or 4 minutes it will start to run on its own without any pedal. Usually after that I have to give it another 3 or 4 minutes to warm up otherwise as soon as I shift it into drive, it dies. So once I get past that point I can drive it as long as I'm cautious not to give it too much gas. If I do give it too much gas for the first 10 mins of driving or so, it feels like its loosing power, starts to cough and black smoke comes out the exhaust. I can back off of the pedal and it will come back to life.

The second problem is the rough idle when at a stop in drive. This problem doesn't show up until the engine is well warmed, especially when the weather is warm outside. When the engine is cold the problem doesn't seem to exist. I'll come up to a stop sign or stop light and everything goes perfect until I reach a stop. Within 10 seconds or so the engine slowly starts to loose rpm and begins to cough a little. It sounds like 1 or 2 pistons are missing. If I step on the gas to move, it will cough severely for less then a second and then pop to life and drive like normal.

Does that still sound like a choke issue? Someone told me I could test for vaccum leaks by spraying carb cleaner around. Have you heard of this???

Usually a choke issue can cause similar issues but now that you have given me some more information there are a couple of things to check. Since this is a carb it pumps fuel all the time to the float bowls. If a float is stuck it will give it too much gas and cause it to run rich because there is too much fuel going into the engine. The black smoke indicates that there is too much fuel going into the engine when you stop. Have you changed the fuel filter recently. It can cause fuel pressure issues and make it hard to start. Once the engine has warmed up it takes less pressure but can still cause stalling issues when you go to stop.

Spraying carb cleaner around the manifold will help you locate vacuum leaks because the leak sucks the cleaner into the engine and will cause it to speed up. Usually a vacuum leak will cause the engine to speed up but it can also cause it to miss.