If the idle speed with the T plate in the proper position over the ports dos not allow enough air. drill holes in the plate to allow additional airflow. Start small but I tend to find a need for a few 1/16 or a bit larger holes. These can be soldered back over if needed.
This will offer a better off idle "tip in"

To test where you are at use a slow opening from closed throttle and listen as much as other senses, I find I have my eyes closed during this phase. When I was learning this stuff was well before widebands which obviously are a superb tool. Hesitations as well as sound changes can guide you to mixture changes in the port transition. A tiny opening of the throttle should be a tiny rpm rise, if the ports are not opening as they should you can detect a non linear rev change and exhaust note. The wideband should backup what your ear hears, very slow opening of idle should have no mixture swing. If the mixture drops or rises with a slight slow tip in the ports are not opening at the correct time.
Till the idle ports are opening when they need to the engine will drive like poo and not respond to reason with jetting. Once you get this transition off idle setup then you go to tuning the size of the idle and main jets,
On the 2.6 with factory manifold you will never get even mixture in all 4 cylinders, not possible. The single carb/ injection is what gives this motor the bad name and low power. Center cylinders run rich, outers are lean, and not even on each end. #1 is leaner than #4. This sucks but it is what we were given.

We did ultimately in the mid-late 70s get sniffers that we stuck a probe up the tailpipe, accuracy was marginal, we stuck to reading plugs, probably a lost art. I think I have lost the art at least. Mind you we had lead in the gas which colored things fast.

FWIW, in recent years I converted to factory dual downdraft carbs on my '72 Colt, the 1600 baby brother to the 2.6. Allot more low end torque than the single carb. After a waterpump failure which I did not recognize till way to late I swapped to an engine that had a shaved block as in the tops of the pistons were cut too, This is along with a well ported and cut head.
Working with the wideband and discovering these Asian market Solexes have 4 stages of idle adjustments, this little car makes so much low end power that I rarely rev over 2500 till you need more in 5th just for road speed, our highways here many times one cruises at 80 which is 4K revs and this car now averages 42 mpg, they only got 26-28 when new. This is all in porting, raised compression and extensive time getting the carbs setup. Waiting for the state to stop spreading the sea water on the roads so I can get back to driving my car.