'90 Ciera SL - Surging idle, then dies, if left idling long enough

It's 1990 Cutlass Ciera SL 4-door sedan with whatever is the biggest 6-cyl engine that ever came in that model (is it a 3.0 or 3.3... can't remember, but I know experts on this car will).

Simply stated, the car is in remarkably good mechanical condition (though could sure use a repainting... fading, etc... but I digress... sorry) and runs pretty good, all-'round. It had started to die and barely run for a while but, believe it or not, simply creating for it a new and better ground connection between the negative battery post and the frame fixed it (apparently some sensor was not getting a good ground or something).

But now there's a different issue, and it's simply this: I can drive it all day long, and it has good mileage, and it will idle fine while in gear and my foot on the brake for the duration of most stop-light waits...

...but if I do something like pull into a parking lot, and put it in park, and just let it idle while I sit and read while my wife's the the store for a few minutes, it will start out idling pretty okay; but after five or ten minutes, the idle speed starts to surge up and down a little... dropping down to where it almost dies and then surging back up above normal idle and then down again to normal idle; then dropping down again after a few seconds... over and over until it usually just dies by itself. Or if I goose the gas pedal a little, and let up, it just drops down to where it's too low and just dies.

I can depress the gas and take it up to 1,200 or higher RPM and it runs, smooth as silk. And after I've done that and if I let off the gas again and let it idle, it idles smoothly for a few seconds... maybe a minute or two, at the outside... and then returns to the surging idle again, and eventually one of the times that it drops down after a surge, it drops so low that it just dies... again.

After this, it also seems like it takes more engine cranks than normal (with my foot completely off the gas) for it to restart. And after I re-start, it runs kinda' okay for a few minutes, again...

...then, again, starts the surging idle thing again.

One guy who was standing next to me while I put a little water into the windshield washer container noticed it and say he had a care which did that once, and it ended-up being some vacuum tube/hose gone bad. And maybe that's the case, here, too... though I'd had to plant that notion in anyone's head, here, and then have that cause them to not contemplate other possibilities... so maybe you should just ignore what I just wrote that that guy said. [grin]

Any thoughts, anyone?

ADDENDUM: After making the above posting, it just hit me that maybe the problem might be that my earlier-improved ground is maybe disintegrating a little or something? Could that be it? Hmm. I'll check that. But I sure would like other suggestions in the meantime. Thoughts, anyone?


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HarpGuy

Ever get it figured out?
I'm chasing a fuel delivery problem as well. When I'm in the stalling mode it dies with extra throttle. I see very rusty metal lines feeding a coffee can sized canister behind the rear wheel on the driver's side. Maybe this has return fuel and is blocked.

My 91 Cutlass with the 3.1 VP holds 43 psi after cranking to 46. When I start the motor it drops to 36. Stabbing the acclerator will make it jump to 46 or so. If this has a vacuum regulator my drop to 36 may be normal. I don't know if it does have a vacuum regulator though.

There was a happy ending at the post titled 91 Cutlass Ciera not starting - no fuel getting thru injectors?.
Apparently he pulled on injector plug after another and found that with one bad one disconnected the car would start and would stall when it was reconnected