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[Solved] Skoda Fabia 1.4 mpi AZE Engine Issue: Jerking at 1200-1600 RPM, Vacuum & Software Problems?

Łuki0601 19917 12
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  • #1 17053319
    Łuki0601
    Level 9  
    Hello. I have a problem with Skoda Fabia 1.4mpi AZE engine code. Namely, jerks at a lower speed of 1200-1600 rpm. The electrician said I had a vacuum problem so I started with it. Head gasket replaced, head made. After this operation, it improved a little, but injection time 3.09-4.12 and negative pressure 360-390 shows on Vag. I replaced the throttle, gas pedal, coil, candles. The problem persists. I called the service and they told me that maybe the software was falling apart. Is it possible? I am asking for advice because I have put too much money into this car
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  • #2 17053336
    Pawel wawa
    VIP Meritorious for electroda.pl  
    Fuel pressure to check. It tugs when it has a high fuel demand.
  • #3 17053378
    Łuki0601
    Level 9  
    3 bar without vacuum 2.5 with vacuum at idle.
    Added after 3 [hours] 41 [minutes]:
    I did not write that the car with LPG. The problem occurs on Pb and LPG. Usually this is the case when I slow down the car to a speed range of 1200-1600 and want to equalize or increase it. Then it starts to jerk. The only thing that saves me at the moment is pressing the clutch and letting the RPM fall to minimum or pressing the clutch and adding gas. After that, the engine runs normally until I have to slow down or raise the engine again in the 1200-1600 RPM range, then the problem returns
  • #4 17054532
    Pawel wawa
    VIP Meritorious for electroda.pl  
    What LPG installation, because I can't see even a vintage car.
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  • #5 17054669
    Łuki0601
    Level 9  
    Year of manufacture 2001. Installation Kme. Only if Pb or LPG are the same symptoms. I drove a bit on Pb itself because I thought it was by LPG but nothing has changed
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  • #6 17055565
    szumi214
    Level 11  
    How long have you been riding on LPG?
  • #7 17055766
    Łuki0601
    Level 9  
    I bought Skode with gas. She made 60,000 on the installation.
  • #8 17055790
    szumi214
    Level 11  
    Check the pressure in the cylinder, gas rings work harder, maybe they are running out.
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  • #9 17056012
    Łuki0601
    Level 9  
    I did it at the very beginning. Pressure 12.5 on each cylinder. As I was replacing the head gasket, I pulled out the sleeves to replace the gaskets under them. Even the edge is not on the sleeves and the honing is original. Nothing gets oil from oil to oil.
  • #10 17056272
    Pawel wawa
    VIP Meritorious for electroda.pl  
    Łuki0601 wrote:
    I drove a bit on Pb itself because I thought it was by LPG but nothing has changed
    You had the bottle turned off? Gas from pipes burnt out? Because if not, it sucks.
  • #11 17056341
    hobbista
    Level 25  
    Łuki0601 wrote:
    Only if Pb or LPG are the same symptoms.
    The common part for these fuels is the ignition system. Replace the coil module for the test. What are your spark plugs?
  • #12 17057983
    Łuki0601
    Level 9  
    New NTG candles, new coil. Gas injectors disconnected. Ie disconnected tubes.
  • #13 17110192
    Łuki0601
    Level 9  
    Problem solved.
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Topic summary

✨ The discussion revolves around a Skoda Fabia 1.4 MPI AZE engine experiencing jerking issues at 1200-1600 RPM, affecting both petrol and LPG fuel types. Initial diagnostics suggested a vacuum problem, leading to a head gasket replacement and head work, which provided slight improvement. Despite replacing components such as the throttle, gas pedal, ignition coil, and spark plugs, the jerking persisted. Users suggested checking fuel pressure, cylinder pressure, and the ignition system, with one noting that the LPG installation might be contributing to the issue. The author confirmed that the problem occurs regardless of fuel type and mentioned that the gas injectors were disconnected for testing. Ultimately, the author indicated that the problem was resolved, although the specific solution was not detailed.
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FAQ

TL;DR: 1200–1600 rpm jerking on a Skoda Fabia 1.4 MPI (AZE); an electrician flagged a "vacuum problem." Triage fuel pressure, ignition, and LPG isolation first; leave software for last. [Elektroda, Łuki0601, post #17053319] Why it matters: This FAQ helps Fabia 1.4 MPI AZE owners—especially with LPG—quickly pinpoint low‑rpm bucking causes and prioritize fixes.

Quick Facts

Whats the first thing to check for 12001600 rpm jerking on a Fabia 1.4 MPI?

Start by verifying fuel pressure during high demand. "Fuel pressure to check. It tugs when it has a high fuel demand." Log pressure while accelerating through 12001600 rpm. Compare requested vs actual using your scan tool or an inline gauge. This quickly separates fuel supply from other causes. [Elektroda, Pawel wawa, post #17053336]

Are my fuel pressure numbers OK, and how should I test them?

Recorded values were ~3.0 bar without vacuum and ~2.5 bar with vacuum at idle. Recheck dynamically while reproducing the jerk. Watch pressure stability as load rises in the 12001600 rpm band. A sag under load supports a fuel supply issue; a steady line suggests looking elsewhere. [Elektroda, Łuki0601, post #17053378]

How do I properly rule out LPG influence when diagnosing?

Edge case: residual LPG can be drawn in on petrol. "Because if not, it sucks." Do this:
  1. Close the LPG tank valve.
  2. Run on petrol until gas in lines burns out.
  3. Test drive on petrol through 12001600 rpm and observe. If symptoms persist, focus on common systems. [Elektroda, Pawel wawa, post #17056272]

Could the ignition system cause jerking on both petrol and LPG?

"The common part for these fuels is the ignition system." Misfire under load feels like bucking. Swap-test the coil module if possible and confirm plug condition and gap. Even new parts can be faulty, so verify under load. Keep the diagnosis focused on components common to both fuels. [Elektroda, hobbista, post #17056341]

Should I worry about piston rings with an LPG car?

A contributor advised a compression test because LPG can stress rings. If compression is low or uneven, mechanical wear is likely. If compression is even, direct attention to fuel, ignition, or vacuum issues. This simple test helps avoid unnecessary parts replacement. [Elektroda, szumi214, post #17055790]

What were the compression results in this case?

Compression measured 12.5 bar on each cylinder. The sleeves showed original honing, and no oil was consumed between changes. Those signs pointed away from ring wear or major mechanical faults here. With sealing confirmed, the focus returned to mixture and ignition control. [Elektroda, Łuki0601, post #17056012]

What do VAG negative pressure readings of 360390 indicate here?

These values appeared along with the jerking. After a head-gasket replacement and head work, the behavior improved a little. That kept the vacuum suspicion alive for this case. Continue checking hoses, connections, and intake sealing during transitions. [Elektroda, Łuki0601, post #17053319]

Do throttle body or pedal replacements rule out air-path faults?

No. The throttle body and gas pedal were replaced, yet the jerk remained. That outcome points back to fuel delivery, ignition quality, or vacuum behavior rather than those actuators. Avoid shotgun part replacement; test each system under the symptom conditions. [Elektroda, Łuki0601, post #17053319]

How can I reproduce the symptom reliably for logging?

Slow the car into 12001600 rpm, then try to hold or raise speed. The jerk typically appears there. Pressing the clutch to drop rpm, or clutching and adding throttle, temporarily clears it. Use this pattern to capture data in your logger or VAG tool. [Elektroda, Łuki0601, post #17053378]

Can LPG injectors or lines cause petrol-mode jerking?

The LPG injectors and lines were disconnected in this case. The problem persisted on petrol. That result suggests the root cause was not the LPG injection hardware alone. Keep attention on fuel pressure, ignition, or vacuum shared by both fuels. [Elektroda, Łuki0601, post #17057983]

Is ECU software a likely cause of this symptom?

A service mentioned possible software issues. However, contributors focused on mechanical checks first. Rule out fuel pressure, ignition components, vacuum integrity, and LPG interference before pursuing software. Mechanical verification prevents unnecessary programming work. [Elektroda, Łuki0601, post #17053319]

What vehicle and LPG details were involved here?

This was a 2001 Skoda Fabia 1.4 MPI (AZE) with KME LPG. The car jerked on petrol and on LPG. That points to systems common to both fuels rather than fuel-specific hardware. [Elektroda, Łuki0601, post #17054669]

I already fitted a new coil and plugs. Should I still suspect ignition?

Yes. New parts were installed here, yet the jerk remained. Load-related faults can persist with new components. Swap-test with a known-good coil or recheck plug condition after driving. Confirm under the exact conditions where the symptom appears. [Elektroda, Łuki0601, post #17057983]

What finally fixed the problem in this thread?

The original poster reported "Problem solved" but did not share the fix. Use the outlined diagnostic flow to reach a verified root cause on your car. [Elektroda, Łuki0601, post #17110192]
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