Hi Roger,
The short answer is: new or re-con injectors required.
I come across this regularly as I repair several taxi’s.
A quantity comparison check will usually not appear too terrible, but a leak back test will reveal a noticeable imbalance.
Your lack of throttle response will be irregular, in so much as some days it may not appear, other days it will be every time the vehicle is started.
This does get worse as time goes by, (not surprisingly) to the extent that occasionally the vehicle will refuse to start on first or even second attempt.
Cheers, Tony.