Truck Repair: 89 S-10 Backfires under acceleration, auto tranny, back fire

Question
Dear Mr. Van,

My 1989 Chevy S-10, 2WD, 4.3L V6, Ext. Cab, Auto Tranny, 203000 miles, is backfiring under acceleration. I have replaced the distributor cap and rotor and checked all the plug connections. Is NOT throwing any codes. I have had checked: O2 sensor, catalytic converter, MAP Sensor, Throttle Sensor, replaced fuel filter, replaced PCV valve, and put all new vaccum lines in. This started after I changed the distributor cap and rotor and sprayed a large amount of carb cleaner on the throttle body to clean it up. I have checked and double checked the new rotor and distributor cap to ensure it was on right and not damaged, I have checked and double checked to make sure the plug wires were correctly put back on. It has always idled rough when first started due to it's age I guess, but it has never backfired at all. When driving especially when first started for the day any medium to hard acceleration will result in a back fire in what sounds like the engine compartment. When warmed up, stop and go traffic or hard acceleration (freeway merging) will result in a backfire. It idles fine when warmed up. I am at a loss, did the amount of junk that went down the throttle body foul something out? I have heard everything from EGR Valve to plugs to the air charge sensor. I honestly haven't a clue at this point. Also, the hose on the drivers side (opposite side of the PCV) coming from the top of the valve cover that leads to the rear of throttle body (looks like some sort breather or something) was corroded and I put a new one on that fit tightly maybe that has something to do with it? Before I go randomly replacing parts my wife said to write to you and get your take on this as you are the expert in this category. I appreciate your time and look forward to your response. Thank you in advance.

Best Regards,

Barton and Jenna

P.S. It never had this problem before I sprayed in the cleaner and changed the cap and rotor.

Answer
Hello Barton,
That last sentence is a strong clue.
The spray didn't damage anything.
If you have the old cap and rotor, I would stick them back on, just to isolate that possibility.
There is an idle air control valve in the throttle body that can usually be cleaned with that carb spray, without removing it.
The throttle position sensor is the item I would want to test again, as well as the fuel pressure, but considering what you say, it was the changing of the cap that started it, so seems like that is where to start.

Van