Hey again everyone.
For those of you who don't already know, I've got an '84 Caprice 4 door sedan w/ the 305 V8, 4BBl Rochester Q-Jet. I just rebuilt the carb about 3 months ago, and since then the car's been running outstandingly well, until about 2-3 weeks ago. Its gotten a hesitation/bog and stumble immediately on accelleration, and clears up after about 1 second. During that 1 second, brown-ish dark fumes come out of the exhaust, which I assume it means a rich mixture. But the dark exhaust goes away as soon as the hesitation is gone. Every once in a while the car runs good, and doesn't do this, but its become more and more common. Air filter is new as well. Any help would be great. Thanks!!

If you are running a computer controlled carb try changing the O2 sensor.

I just replaced it 2 months ago.... could it have gone bad that quickly? Its a Bosch.

I just replaced it 2 months ago.... could it have gone bad that quickly? Its a Bosch.
Bosch...yes. People have had serious issues with their O2 sensors.

What should I get in place of a Bosch?

For the O2, go with ac delco replacement.

Bad EGR valves can cause an off idle hesitation. But the brown smoke means you are running rich. Could be the power valve or accel pump. Choke could be closing. You should take a good look at the carb looking for anything that came loose. Check the float level, too.

//2000CAYukon

Have you checked your ignition system? A distributor will give intermitent problems with weak spark or no spark at a given moment.

I had problems with my HEI in that respect and after replacing it with an MSD Ready to Run distributor have no more problems.
And, before you ask, no I do not run a computer, I did away with that problem prone mess as well.

I f you have the CCC carb (computer command control), you need to set your mixture control solenoid dwell. When not set correctly, this will create (sometimes severe) a hesitation, stumble condition an acceleration. You'll need the proper scan tool & carb tools to make this adjustment.

Last week I filled up my tank. In 4 days I drove about a total of 50 miles, and used up nearly the whole tank. I have absolutely no gas leaks whatsoever, the car was running incredibly rich. I had no power at all, and needed to give it 3/4 throttle just to keep it moving at about 50 mph. So I decdided ta go with the simplest thing first... the O2 sensor. It took a few stores, but I found an AC Delco one ($40.00) at Nu Way Auto. It solved all of my problems.... the car was once again very responsive, has great acceleration, and ta keep it moving at about 60 mph I barely have to touch the throttle. Oh, and best of all, I'm getting insanely good gas mileage (driven about 20 miles so far, and haven't even used 1/16 of a tank).

I've only encountered one problem so far... if I let the car idle for too long (a minute or 2) the check engine light comes on, but goes away when I start driving again. It comes up as a code 44, which my Hanes book says lean fuel mixture. Do I need to adjust my idle mixture screws?

Oh, and by the way... thanks everyone for your suggestions!