Berryman makes a fuel system cleaner B-12 (#0116) and on the back of that can says to use B-60 for neglected fuel systems.
Use Berryman's B-60 (#7516) High Mileage Fuel System Rejuvenator in gas tank to deep clean out varnish, etc.
It was the only treatment that worked (short of car mechanic professionally cleaning fuel injectors).
My idle fuel use is now lower as gas is not just pouring into the cylinders.
Available from NAPA for $22.69 / kit (an oil additive #7517 is included in kit, contains Synthetic Blend Motor Oil with Moly). I didn't use #7517.
It can be ordered online or in-store and picked up next day in-store. Give them a phone call. You can use your AAA member discount at NAPA.
Also you have / had oil coming into your air intake plenum via the PositiveCrankcaseVentilation valve and its tubing.
This causes deposits in the intake manifold at the valves and clogs the catalytics.
This can happen when too much oil is in the engine (after not changing motor oil & then over filling). Fuel dilution of motor oil may occur due to fouled / partially clogged injectors (not misting correctly).
The PCV valve is located on the top rear driver's side of the engine and the hose goes forward and into the top front of the intake manifold.
The hose then comes out near the vapor canister purge valve* and goes into the front of the air intake plenum*.
I found some oil pooled mid-plenum leading to the throttle body valve.
Clean out the oil in the plenum tube with paper towels and clean the throttle body and flap.
Don't leave anything behind or it will be sucked into air intake manifold!
Note: * If either of these leak, they mess up your air / fuel mixture as they are after the mass air flow sensor (vacuum leaks).
The 1st: ACDelco GM Original Equipment 214-1685 Vapor Canister Purge Valve with Bracket is at Amazon.com (I reused the old bracket & adapter to install)
and the 2nd: air intake plenum PCV nozzle can be fixed with Shoe Goo (seals & glues plastic) $5 at Walmart (Also can re-glue old tail light housings, etc.)
Carefully take off the plastic-welded intake plenum PCV hose nozzle at its base, clean with paper towel & reattach securely.
Slip on and attach hose after a few minutes. Hold intake plenum PCV nozzle in place with a spacer and duct tape, etc. You can then drive about.
Shoe Goo sets up quickly and cures in ~24 hours & remains flexible (shoe sole, etc. repair).
Do NOT apply flame or high temperature. The next day, remove the tape, etc.
Odds are you have carbon deposits in the intake manifold about the intake valves.
A major professional chemical cleaning operation with chemicals or walnut shell media blasting. (I have not done this yet.)
Other problems: Check all 3 of your engine & the 1 transmission mounts. Also check / replace the sway "bar" bushings. My mounts / bushings had failed.
My failed bushings were covered with black RTV (useless). I replaced them, too.