Originally Posted by Diesel911

The situation with buying Injectors from a parts place is that they have a big Bin with 100s of Injectors in it. When they need 6 Injectors they reach in and grab 6 Injectors. So you have to view them as 6 individual Injectors.

The "default spec value" for the Pop/Opening Pressure of your Injectors is 135bar (1957.5 psi) to 145bar (2102.5 psi). So the Injectors that they pull out of the box can be anywhere in that range. That means there could be a difference of 10bar (145 psi) between the lowest and highest pressure of the 6 Injectors pulled from the Bin.

However, in the past the Factory has recommended that difference between the Pop/Opening pressures from the highest to the lowest Pop/Opening pressures on the Injectors on the Engine to be a max of 5bar (72.5 psi).

When Injectors from one Engine are rebuilt in a shop as a set they try to get that difference to be even lower. The 2 Member that rebuild Injectors for other member try to keep the difference to 3bar. (This can sometime be difficult to do as the Pop/Opening Pressure is adjusted by exchanging different sized Shims to change the Pressure Spring Tension; sometime you cannot find the right thickness of Shim you need to get the pressure you want.) They call this a "balanced set".

So what the other member was saying is that your chance of getting a balanced set from Injectors grabbed from a parts bin is slim and to take them someplace local and have the Pop/Opening pressures checked to see if they are balanced to each other.
A has a better potential to idle smoother.

The above being said the problem you are having may be from a tiny particle of dirt getting in the Injector or a defective sticky Injector Nozzle.
If you can do so while the Engine is exhibiting the problem loosen and tighten 1 Injector Hard Line Nut at a time.
If they Injector nut you loosen causes little or no change in the Symptoms; that is the faulty Injector (sometimes you can also watch the Engine RPMs on the Tachometer). If you loosen the Injector Line Nut on a good Injector it will have an immediate and obvious effect (the RPM will obviously drop). In fact Most of the good Injectors should have a similar RPM drop or produce similar Engine shaking when the Injector Line Nut is Loosened.

If you locate a problem Injector call or Email the Seller and tell them you have a Faulty Injector and I bet they will send you an Exchange