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[Solved] vw polo IV 1.2 12V 9n - jerking the car while driving, the car goes out on w

GROSS AVOS 27342 11
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  • #1 17127532
    GROSS AVOS
    Level 9  
    Posts: 9
    Rate: 5
    contaminated fuel falls out, water in the fuel also.
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  • #2 17128087
    koks110
    Level 10  
    Posts: 64
    Rate: 11
    Dirty stepper motor, HV cables to be replaced or candles. Fuel injection failed, fuel pump defective. There are many possibilities.
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  • #3 17128098
    Anonymous
    Level 1  
  • #4 17128106
    koks110
    Level 10  
    Posts: 64
    Rate: 11
    I do not know this model, probably does not have it?

    Added after 3 [minutes]:

    I wrote only the possibilities that can be such a jerking, can also be a temperature sensor that is located on the engine.

    Added after 2 [minutes]:

    Bieda z nędzą wrote:
    koks110 wrote:
    Dirty stepper motor

    If you were aware of the nonsense you wrote, you probably buried under the ground and sowed grass in the place of burying. There is no such thing there, and even though it is, it does not affect it.
    koks110 wrote:
    HV cables

    There are no HV cables there, the coils are put directly on the candles.


    So if there are coils mounted there must be connected to the computer and check if there is no ignition on one of the cylinders. If you don't need a reason, look elsewhere :)
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    #5 17128309
    Adam5502
    Level 10  
    Posts: 196
    Help: 2
    Rate: 31
    Colleague, I suggest you connect a car under VAG, repair in style, maybe I will replace it or maybe it ...... It is a waste of your time and money. If you want to repair and diagnose a fault yourself, the cheapest Obd2 interface costs PLN 40 laptop and you already know what hurts your Polo and the interface remains until the next failure.
  • #6 17136194
    GROSS AVOS
    Level 9  
    Posts: 9
    Rate: 5
    I was at the mechanic who found the throttle dirty. the throttle was very dirty, after disassembly I cleaned it is now as clean as the back of the baby. There is no stepper motor, there is a module, these are the words of the mechanic. I exchanged candles for my own peace.
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  • #7 17142502
    GROSS AVOS
    Level 9  
    Posts: 9
    Rate: 5
    I don't have an interface, neither is the software, so a mechanic. The computer displayed problems with the MAP sensor, ignition loss on subsequent cylinders. After clearing the errors, I traveled about 20 km, the computer did not show any errors, I came home. the next day, disappointment, goes out at low speed, jerks and it is not known when after a dozen or so meters or kilometers it falls on low speed does not respond to the accelerator pedal.
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    #8 17142801
    Adam5502
    Level 10  
    Posts: 196
    Help: 2
    Rate: 31
    Buddy pay attention to the coils in what condition they are, if you have the possibility of substitutions. Just like colleague koks110 above prompted. a spark appeared. The integration of the ignition system with the injection system allows cutting off the injection into the cylinder with the detected lack of ignition.
  • #9 17158930
    GROSS AVOS
    Level 9  
    Posts: 9
    Rate: 5
    I went to the next mechanic, he unscrewed the candles and said that the candles are wet, which means that the "injection" was pouring out, he applied coils to the unscrewed candles and watched the spark jump on the candles located on the engine while turning the starter. The computer lost ignition on the second cylinder. I replaced the injections with new ones, the coil on the second cylinder and for my own peace the first and third. This brought the effect that it stopped dying at idle, on a cold engine it still jerks, on a warm one, but still after driving a dozen or so meters or kilometers it stops responding to the gas pedal. the exhaust light comes on sometimes, not always and after a while goes off.
  • #10 17250181
    GROSS AVOS
    Level 9  
    Posts: 9
    Rate: 5
    The next mechanic found the mixture error too poor, often the reason is the poor fuel pressure said that the pressure should be 3 bar and the pressure in the manifold 300 mbar. The pump tested the waveform with something using an oscilloscope so he did not fit the fuel filter and the pump. I was not surprised because he is a mechanic with decades of experience and a very good equipped workshop. He wanted to get to the timing and said that he could jump the chain or pull up then there is less power and more combustion, the catalyst may be clogged and the exhaust outlet difficult. He stopped at the pump and filter, it was better. After driving a hundred kilometers is even worse when you press the gas pedal is suffocating, you should increase the speed very slowly then it will go.
  • Helpful post
    #11 17250214
    sokarsg-1
    Level 11  
    Posts: 139
    Help: 1
    Rate: 35
    Buddy in this engine often jumps the timing chain (in the version of the engine produced until 2005 later VW graciously improved it). Unfortunately, the chain jumps on the roller on which there is no hall sensor, therefore the computer does not detect it. Organoleptically, this can be checked by unscrewing the two end caps in the battery-side head. After shifting, both rollers should be perfectly horizontal, and it is best to screw in the locks intended for this http://allegro.pl/blokada-rozrzadu-vw-polo-1-2-6v-12v-azq-bme-i7356503607.html#imglayer these two on the left.
  • #12 17280445
    GROSS AVOS
    Level 9  
    Posts: 9
    Rate: 5
    By word of mouth, I found a real mechanic, he sat over the car for three days, replaced all the sensors including the engine controller and nothing came of it, so he started from scratch, from the injections, the injections were new and this information confused him after the wine number came that new injections for such an engine but the number of holes and the color marking on them did not match the driver. After putting on the right car like new, this information cost me almost two thousand zlotys. The solution to my problem is INJECTION.
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Topic summary

✨ The discussion revolves around issues with a VW Polo IV 1.2 12V (9N) experiencing jerking and stalling while driving, particularly at low speeds. Initial suggestions included checking the fuel system, ignition coils, and throttle body. A mechanic identified a dirty throttle and issues with the MAP sensor and ignition loss on cylinders. Subsequent diagnostics revealed wet spark plugs indicating fuel injection problems. Further investigation pointed to potential fuel pressure issues and timing chain problems, which could affect engine performance. Ultimately, replacing the fuel injectors resolved the issue, highlighting the importance of using compatible parts for this engine model.
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FAQ

TL;DR: 2,000 PLN later, "The solution to my problem is INJECTION." On a VW Polo 1.2 12V, mis-matched injectors caused jerking, stalling, and throttle loss; correct ECU-matched injectors fixed it. [Elektroda, GROSS AVOS, post #17280445]

Why it matters: This FAQ helps VW Polo 9N 1.2 12V owners quickly pinpoint jerking/stalling causes and avoid wasted parts swaps.

Quick Facts

What actually fixed the jerking in this VW Polo 1.2 12V case?

Installing correct, ECU-matched fuel injectors fixed it. The car had new injectors, but with different hole count and color code. After matching injectors to the engine control unit, the Polo drove like new. The owner’s spend was about 2,000 PLN. "The solution to my problem is INJECTION." [Elektroda, GROSS AVOS, post #17280445]

How do I confirm my injectors match the ECU on a 9N 1.2 12V?

Check via VIN-based parts lookup, then compare nozzle hole count and color markings to ECU expectations. In this case, new injectors didn’t match those parameters and caused severe drivability issues. Fit the exact injectors specified for your ECU. [Elektroda, GROSS AVOS, post #17280445]

How do I quickly diagnose jerking/stalling with VAG/OBD at home?

Buy a low-cost OBD2 interface (~40 PLN), connect a laptop, and run VAG-compatible software. Read stored faults, record freeze frames, clear codes, then road-test and rescan. This avoids guesswork and saves money on random parts. [Elektroda, Adam5502, post #17128309]

Why does the engine cut fuel to a misfiring cylinder?

"The integration of the ignition system with the injection system allows cutting off the injection" when misfire is detected. This limits catalyst damage and raw-fuel washdown. A bad coil can trigger this cut, causing jerks. [Elektroda, Adam5502, post #17142801]

Does this Polo engine use HV ignition leads?

No. It uses coil-on-plug, with each coil mounted directly on its spark plug. There are no separate high-voltage cables. [Elektroda, Anonymous, post #17128098]

Is there an idle stepper motor on the Polo 1.2 12V?

No. It uses an electronic throttle module. A very dirty throttle body caused stalling at idle; after cleaning, idle stabilized. [Elektroda, GROSS AVOS, post #17136194]

MAP sensor faults and throttle non-response—are they linked here?

Yes. The ECU logged MAP sensor issues and cylinder misfires. The car then stalled at low speed and sometimes ignored the accelerator pedal. Clear codes, drive, and rescan to confirm root cause. [Elektroda, GROSS AVOS, post #17142502]

What fuel pressure and manifold values should I expect?

A competent mechanic targeted ~3 bar fuel pressure and ~300 mbar intake manifold pressure. Low pressure or a clogged filter can cause lean running and suffocation on throttle. Address the pump and filter first if readings are off. [Elektroda, GROSS AVOS, post #17250181]

How can a shop verify a weak fuel pump without pulling it?

They can analyze the pump’s electrical waveform with an oscilloscope. In this case, scope readings indicated pump and filter issues, guiding replacement decisions efficiently. Ask for a scope-based assessment under load. [Elektroda, GROSS AVOS, post #17250181]

Can the timing chain cause jerking without setting fault codes?

Yes. On early 1.2 engines, the chain can jump on a gear without a Hall sensor, so the ECU may miss it. "In this engine often jumps the timing chain." Verify alignment mechanically if symptoms persist. [Elektroda, sokarsg-1, post #17250214]

How do I check timing chain alignment on the 1.2 6V/12V quickly?

  1. Remove the two end caps on the battery-side head.
  2. Set the engine at TDC and check both cam rollers are horizontal.
  3. Install the specified locking tools to confirm alignment before further work. [Elektroda, sokarsg-1, post #17250214]

Could contaminated fuel or water in fuel be the cause?

Yes. Contaminated fuel, including water, can cause jerking, stalling, and poor response. Drain suspect fuel, replace the filter, and refill with fresh fuel. [Elektroda, GROSS AVOS, post #17127532]

Should I clean the throttle body if my Polo jerks or stalls at idle?

Yes, if inspection shows heavy deposits. A very dirty throttle body was cleaned, and idle stalling stopped. Remember, this car uses an electronic throttle module, not an idle stepper motor. [Elektroda, GROSS AVOS, post #17136194]

How can I check coils and spark without special equipment?

Remove spark plugs, connect coils to them, and crank the engine while observing spark. Here, the ECU also logged ignition loss on cylinder two. Replace the faulty coil or swap positions to confirm. [Elektroda, GROSS AVOS, post #17158930]
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