Audi 80 B4: Cold Start & Idle Control Issues

Hello there,
I would like to get your opinion on the following problem.
When starting the engine cold, it runs roughly, as if only three cylinders are working.
Preheating is okay, all glow plugs have been checked and are in good working order (each draws approximately 20A at the beginning of the preheating process).
The idle cut-off control shows that cylinder 3 is weak immediately after starting, with a difference of over 5 mg per injection compared to the other cylinders. When warm, cylinder 3 remains slightly weak, but within tolerance, with a difference of approximately 0.8 - 1.2 mg per injection, depending on the operating conditions.
The injectors are designed for a mileage of 100,000 km. I noticed the slight weakness when the engine is warm from the beginning with this set of injectors.
It seems to be related to cylinder number 3.
It is not possible to swap the injector of cylinder 3 with that of another cylinder (injector with NHG). Swapping the pressure relief valves of cylinder 3 and cylinder 1 (cylinder with the highest output at idle) did not yield any results.
Valve timing is correct, with the electronic distributor essentially in its default setting, which is slightly late but still within the acceptable tolerance range (for years).
The compression has been recently checked and is between 24.6 and 25.2 bar with a warm engine. The car has 340,000 km on the odometer, with the cylinder head gasket replaced 100,000 km ago.
Could the problem only be with the fuel injector for cylinder 3, or could there be another cause? The fuel injection pump shows some signs of age - the MSW (Mass Air Flow) sensor has been cleaned three times now, at intervals of 40,000 km. The injection timing, as measured by the "Istwert" (actual value) in diagnostic code MWB4, is too early at idle or with light load.
Best regards,
Herbert.

Hello Herbert,

Okay, remove the NHG (presumably a type of component) and replace it... if the nozzle is bad, just put in a new one.

Best regards, Rainer.

Hello,
I have now had the injector for cylinder 3 (with NHG) professionally cleaned, and also had a second injector from my own machine cleaned as a reference. First, the visual condition. The injector with NHG is clean at the tip and almost free of residue. The reference injector has slight deposits. The engine has been running on rural roads and in the city for the past two weeks, so it has been driven more conservatively.
"Injection pressures: Nozzle with NHG 180-185 bar, reference nozzle 175-180 bar. The new value is 190 bar, and the wear limit is 170 bar. The atomization pattern is flawless for both nozzles at low flow rates. At high flow rates, the atomization of the nozzle with NHG appears somewhat uneven in one or two of the holes; you can see something like an edge jet in the conical spray."
According to the technician, both nozzles are sealing well (audibly), and the behavior of the nozzle with NHG is not yet a reason for replacement.
Could the observed fuel spray behavior, especially during cold starts, and a potentially excessive initial injection volume still be the cause of the problem? I'm hesitant to replace the expensive injector based on suspicion alone, given the otherwise good results.
The different values for the idle speed control could also be partially caused by overshooting of the mass airflow sensor. It is prone to becoming dirty, but it was only cleaned in the fall.
Best regards,
Herbert.

Hello,
Final feedback: The cause of the frequent misfires during cold starts was likely the glow plug connectors. After I replaced the connectors (because the insulation was cracked), there were no more misfires, even in freezing temperatures.
The old plugs were actually still quite tight, but that might have been caused by the insulation.
If this was the error, it could only be detected by measuring the current flowing through the candle with a clamp meter. Using an ammeter directly in the circuit won't reveal the problem because you're ensuring a good connection.
The new connectors can be attached using a wire connector crimping tool or by soldering. Part number: 443 971 994, housing (which has been discussed in the forum before).
Best regards,
Herbert.