From your profile, I assume you have a Mk1 Golf. My brother has a Mk2 and his airflow meter is the older flapper type. Inside there a flap that progressively opens on increased airflow, and this changes the voltage the ECU see.
If you think that there are 3 elements that make your car start, run and accelerate - air, fuel and spark, it's as simple as that. Generally air is not a problem unless you have a nest hampster in your intake! However, ensure the filter is not overly blocked.
If it's generally running ok, then one could assume that the spark is always present. This could be weak and at certain points causing a lack of power. Have you changed these. I work on MX-5s and these get a hard time and a simple plug change can cure a problem. Whilst you have them out, take a look at the colour of the plugs, do they indicate the mixture is lean (lack of colour and glazed)?
The more complicated tests involve the fuelling. If the mixture is lean then for some reason the engine isn't getting enough fuel, and this could be down to a number of reasons. Without being rude, this is beyond most mechanics, who generally guess at what is wrong and you end up changing parts in an attempt to try and resolve the problem. You could have low fuel pressure, the airflow meter is not reporting voltages properly, dirty injector, incorrect Lambda reading. Your really need some equipment to test this, plus some additional information. Do you know what sort of fuel pressure is normal at wide open throttle or the vacuum line disconnected from the fuel pressure regulator? You could log the voltages from the airflow meter at different loads and see if the information is correct. If it's like our 1600 MX-5 it works on a 0-5v range, the higher number low load and idle, the higher the load the lower the voltage (later MAS type airflow meters work the other way around). I guess the diagnostics would throw a code for the Lambda sensor? On high load you should see a voltage of around 0.8volts.
Does that help?
Phil
