Likely cause of poor performance at low RPM but normal at higher RPM?

Question

For a fuel injected, in-line three cylinder 1.0 litre gasoline engine (specifically X10XE I3 found in Opel Corsa B), what is the most statistically likely cause of the following problem, and what checks (if any) should be performed to investigate the problem further, to narrow the possibilities?

• Poor performance at low RPM.
• Normal performance at higher RPM.

By "poor performance" I mean there is a "hole" in the power curve of the engine. At wide open throttle starting from low RPM, the engine will at first start to make power, then hesitate and deliver no performance at all. RPM will still build up, until it reaches higher RPM where the performance is normal.

This is a weak engine by design but the normal curve of it certainly doesn't feel like this.

There are no bad engine sounds during idle nor acceleration. Idle is fine. There is no visible smoke from the engine nor exhaust. The ECU has not lit any ECU warning lights.

The age of the engine is 17 years. It should be noted the engine has been driven at unusually low RPM for these 17 years, if this matters. It probably never saw high RPM and especially not higher RPM and WOT at the same time. Driven ~45 000 miles. Service schedule followed.

No attempts at repair has been made, OBD has not been checked.

Answer 1

Before everything else i would check the spark plugs. Under certain circumstances a crack in the insulator can cause problems at low rpm's but would be not feel-able with high rpm's.

Edit, and greetings to DucatiKiller: Sorry, no explanation for the root cause. However, this comes from personal experience: I had a comparable problem (stuttering engine) at another car. The result was that the insulator of one spark plug was cracked, after changing the plugs the engine was ok.

I recommend to check the spark plugs first because this is the most easy thing to do and a possible root cause. So the work/reward ratio should be good.

How to do it:

1. Let the engine cool down.
2. On top of the engine remove the small plastic cover covering the ignition module.
3. Remove the two inhex bolts
4. Disconnect the cable to the module.
5. Cautiously remove the ignition module, do not lift the module one-sided. It will require a bit of force.
6. Remove the spark plugs (16mm socket).
7. Check the spark plugs: Has the insulator visible cracks? Is the color of the insulator uniform or are there any spots visible? Check the color and appearance of the plug, use this site: NGK
8. Check the electrode gap: According to Opel you need 0.9-1.1mm. NGK, however demands 0.8mm. So please take these values with a grain of salt.
9. If necessary replace the plugs: You need 3 x BKR5EK (NGK) or comparable plugs.
10. Tightening torque: 25NM for the spark-plugs, 8NM for the bolts in the ignition module. Torque values are for a cold engine.

Answer 2

There are multiple things that could cause this, although I would start with the air metering device. I'm not familiar with this engine, but if it is electronically controlled then it likely has a MAP (manifold absolute pressure) sensor or a MAF (mass air flow) sensor. I would test whichever this engine has. The Map sensor will likely be easier to test then if equipped with a MAF sensor- failing one of these being bad I would look at the timing if it is adjustable. The timing could be retarded slightly causing poor performance at low RPM but regular performance at higher RPM, however usually the idle would be effected by this as well.