TDI: Intermittent Power Loss - Troubleshooting

Hello everyone,

I'm having the following problem with my Golf III TDI, manufactured in 1996, with a 1Z engine and approximately 200,000 km on the odometer:
Seit ca. 1 Jahr verliert der Motor beim Beschleunigen ab ca. 110-120 km/h plötzlich an Leistung. Der Gang (Drehzahl) scheint keine Rolle zu spielen, das Problem tritt vom 3-5 Gang auf. Das wirklich Unangenehme ist, das der Fehler nicht immer auftritt. Ist der Motor kalt hat man öfters Glück und er läuft wie gewohnt. Beim warmen Motor that man in ca. 90% aller Fälle Pech und 'schleicht' (Höchstgeschwindigkeit auf gerader Strecke ca. 140) dahin . Aber seit es draußen etwas wärmer und trockener ist, tritt der Leistungsverlust etwas seltener auf. Alle 'Wissenden' die ich befragt habe, sagen pauschal: 'Luftmassenmesser'. Die VW-Werkstatt sagt hingegen: 'Luftmassenmesser i.o. aber Stuergerät defekt -> nacheinander alle Komponenten tauschen, usw. ' Der Kraftstoffverbrauch hat sich nicht verändert. Kann wirklich das Steuergerät defekt sein ohne dass man sonst irgendetwas davon merkt (Vorglühlampe, Ruckeln, etc.)? Oder kann der Luftmassenmesser sporadisch ab einem gewissen Luftdurchsatz falsche Signale liefern, abhängig von Umgebungs-(Motor)temparatur und Luftfeuchtigkeit? Wer hat eine Idee oder kennt diese Problem? Thank you in advance!
Greetings.
Felix.

Welcome, and it's great to have you here.

There's a button here that says 'Search.' If you type 'performance loss 1z' there, you'll find a lot of reading material. It's a very popular topic.

Hello,

I've read quite a bit before asking my question and found a lot of interesting information. However, none of the problems described so far match mine. There's an article that describes a similar problem, but in that case, the performance loss is speed-dependent. So, does anyone have any ideas and can help me? Or does anyone have a kind of checklist that I can follow systematically?
Greetings.

Hi,

Without additional measured values from a test drive using VAG COM (or a similar tool), it's pure speculation to talk about any potential defects. A log file containing values for boost pressure, air mass, etc., would be very helpful.
I find it very unlikely that a problem with the engine control unit (ECU) would cause a lack of power.

Regarding the 1Z engine, if you experience a lack of power, I would initially suspect a problem with the turbocharger's boost pressure due to a faulty boost pressure control system. The control valve (located near the fuel filter) is prone to failure, which can cause the boost pressure to remain stuck at a maximum of 0.6 bar (instead of 0.9 bar). This issue can also occur intermittently.

Okay, I've found at least 20 articles that might address your problem.

But never mind. What about measurements of boost pressure and air mass? Without those, it will be difficult to make a reliable assessment. My suggestion: check the mass airflow sensor, or look for a stuck EGR valve, or a faulty boost pressure control system.

A faulty control unit is excluded.

edit: Bertil was probably faster .