Rough Idle, '84 Caprice, 305

DWCaprice2017

Not-quite-so-new-guy
Oct 25, 2019
13
3
3
Hi, Everybody!
I got the car almost five years ago. About a year-and-a-half ago, I had the carb (electronic Quadrajet) rebuilt. It ran fine for about four days, then it could barely stay on. Back at the carb shop, he rebuilt it again, finding some small particle had lodged into something. Fixing that, the car ran well...until about two months ago, when it barely stayed on to get me to work. Back to the carb shop, he told me it was dirty--sucking up the junk in the tank--I wasn't keeping much gas in the tank, now I am. He cleaned it, put in a new filter, this time he mentioned that he thought something might be off in the distributor--without specifically testing it. I drove the car for a few days, it was actually running a bit rougher now than before the third rebuild. Doing research, I discovered that a faulty Ignition Control Module could cause rough idling, a bad/clogged EGR could cause it, and of course, the spark plugs, which I replaced about two years ago. I'm taking the bus to work now, so I only drive it a short distance to keep the battery charged once a week, the engine sounds great!

I've replaced the spark plug wires, cap, coil, and rotor when I did the spark plugs. For all these, when possible, I use AC-Delco.
I know the left (passenger side) valve cover gasket needs to be replaced, I did the easier right one a couple years ago. I know it's seeping oil, causing smoke.

Questions:
1. Wouldn't a fuel filter--the one that goes into the carb--filter out all the junk in the gas tank?
2. Is there another component that I hadn't listed that could cause a rough idle--presuming there's no vacuum leaks?
3. Could the carb just be beyond rebuilding, and just get a replacement?
4. I was told to only use Shell or Chevron gas--I'd been using Arco, big mistake I now know!
I took the car to a smog check (California), he gave a preliminary check, it was on the border of not passing,
he suggested I use CRC's Guaranteed to Pass, which I plan to use after getting the idle fixed--does this
stuff work?

Thank you, all!
Be safe out there!
 

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