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The car is Opel Astra H (2006, 1.6L). I'm having problems with this as the symptoms don't appear all the time so it's hard for a mechanic to diagnose. Since i bought the car i had slight problems with the car accelerating poorly, especially on lower gears. Sometimes running the car from stop position on gear 1 resulted in worse acceleration than a bicycle. The car was shaking when driven very slowly (1st and R gears) when applying the clutch. I thought the clutch was slipping so i had it replaced and it's much better now - the symptoms occur less often, but still there's something wrong.

  • The car is shaking sometimes when driving very slowly and applying the clutch (happens rarely)

  • The car will accelerate extremely bad sometimes when moving from stop position in 1st gear (just like it would start from 2nd or 3rd gear) - (happens very rarely but can be dangerous)

  • The car will jerk just a little bit when driving at normal speed and changing gear (after releasing the clutch) (happens quite often - doesn't bother me all that much, but might be connected somehow)

  • You can feel that sometimes the car is not accelerating properly or good enough especially in lower gear range (1-3). One mechanic told me while driving and checking it out that this car won't do any better (it's 105 HP), but i can feel it doing better sometimes (it's 50/50 chance to get either experience).

What should i do, how can i diagnose properly? I had suggestions it might be the camshaft of crankshaft position sensor that might be involved here. Is there a way to diagnose without taking the engine apart?

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    From your description, this sounds like a driving problem, not a vehicle problem. I can't tell you how you are currently driving your vehicle. On a manual transmission vehicle, you have to slip the clutch more at the beginning of your go from a stop or the car will just not pick up speed very quickly. If you aren't consistent with this, it can seem as though the car is only doing it irregularly. Also, shifting into the next gear at the incorrect times can feel the same in the upper gears.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Jan 10, 2021 at 14:33
  • The description in low gear sounds like kangarooing.
    – Weather Vane
    Commented Jan 11, 2021 at 16:15

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You need to look very closely at the engine RPM during these events. From your description, it sounds like your engine is about to stall out -- meaning you put it in a higher gear than it wants to be.

For a petrol engine, you want to be around 2k RPM normally. Peak efficiency RPM for petrol engines is quite high, I believe it's even higher than 2k RPM. The reason is that petrol engines can't really pull harder at a given RPM. In a diesel engine, you can just inject more fuel and the engine will pull harder.

Honestly sounds like a weak engine combined with bad driving. Your throttle body is very likely dirty too, making your engine idle weakly.

Just give 'er more gas.

If, on the other hand, you do know how to drive, then it can be a couple of things. Many of them are quite hard to diagnose over text, but with powertrain-related problems you always follow the 4-stroke cycle: suck, squeeze, bang, blow.

  • Suck: Is the fuel supply restricted? Are the injectors clean?
  • Squeeze: Do your cylinders leak? Do a compression test.
  • Bang: Do you get detonation in all cylinders?
  • Blow: Is your exhaust system plugged? Catalytic converter failed? Feel your tail pipe exhaust. Listen to it.
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