VW Polo Diesel Power Loss & Rough Running Fix Guide

Had almost identical issues with my 2002 VW Golf diesel last year. Have some experience with basic maintenance, but needed professional help for this one. The symptoms match exactly what I experienced, poor fuel economy, rough running, and reduced power. The engine management system was showing signs of a rich mixture condition, which turned out to be caused by a faulty injection valve. Took it to a workshop where they diagnosed a defective injector that was causing uneven fuel delivery. The repair involved: Complete injector testing, Replacing the faulty injector, Recalibrating the fuel system, Clearing fault codes Total cost was 515€ including parts and labor. The difference in performance was immediate, smooth acceleration returned, fuel economy improved significantly, and the check engine light cleared. To help diagnose your specific case, could you share: Current mileage, When was the last fuel filter change, Any recent work on the intake manifold or air filter, Are there any other warning lights besides check engine, Have you noticed any unusual exhaust smoke color These details would help confirm if your issue matches what I encountered. Given the age of these VWs, injector problems are fairly common, but best to rule out simpler causes first.

Last service was at 132000km, just a couple months ago. Thanks for sharing your experience. After reading your reply, I checked the exhaust and noticed dark smoke, especially when accelerating. The fuel filter was changed during the last service, but the air filter looks quite dirty when I checked it today. The strange thing is the engine starts perfectly fine when warm, but struggles more in cold starts. No other warning lights besides the check engine light. Given what you mentioned about the injectors, this makes sense as a potential cause. Since the last service also included a new oxygen sensor but the issues persisted, I am inclined to take it to a specialist to check the injection system. Would rather fix this properly than risk damaging the catalytic converter from running too rich for too long.

Thanks for the update and checking those items. The dark smoke combined with cold start issues further points toward an injector problem, similar to what I experienced. My Golf also showed those exact symptoms before the repair. The dirty air filter you found could contribute to the rich mixture condition, as the engine computer might compensate with excess fuel. However, given that your oxygen sensor is new and the issues continue, the injection system is still the most likely culprit. My case started similarly, perfect warm starts but problematic cold operation. The workshop explained that worn injectors often show their worst symptoms during cold starts when fuel atomization is most critical. Before taking it to the specialist, replacing that air filter would be worthwhile, its a relatively cheap fix that helps the overall fuel economy and engine performance. But realistically, based on the symptoms and my experience with these VW diesels, you will likely need injector work to fully resolve the issues. Protecting the catalytic converter by addressing this promptly is smart thinking. My repair costs might have been higher if I had waited longer. When you visit the specialist, ask them to perform a complete injection system pressure test, this identified my faulty injector quickly.

The symptoms you described and my inspections definitely point toward injection system issues. The dark exhaust smoke I found when checking and the cold start problems match what you experienced with your Golf. Just ordered a new air filter since I spotted it was dirty, but agree this is probably just a small part of the problem. The fuel-air ratio seems off even with the new oxygen sensor, so getting the injectors tested makes sense as the next step. Since the air filter is cheap and easy to replace, I will do that first. But I have already called a diesel specialist for next week to check the fuel injectors and run those pressure tests you mentioned. With both the intake manifold and catalytic converter being expensive parts, definitely want to solve this before it causes more damage. The 515€ cost you mentioned for the injector work is helpful to know, gives me a rough idea what to expect if it turns out to be the same issue. The similarities between our cases are quite striking, especially the cold start troubles and dark smoke. Really appreciate you sharing your experience in such detail. Will update once I know more after the specialist visit. The thorough testing you suggested should help pinpoint if worn injectors are indeed the root cause here.