What year is the car (the astra has been around a long time with lots of different engines).
The usual cause of this problem is an oiled up idle control valve and throttle body, fairly easy to strip and clean (dependent on year), nothing to do with the brakes, but as well to check the following:-
When was the car last serviced? (At the very least check the air filter).
Does the engine idle and run ok and what RPM does it idle at?
Does it feel like the engine's running ok when driving or is it underpowered, holding back, misfiring or anything?
What happens when you're sitting still with the engine running and press the brakes?
What happens when you rev the engine to around 3000 RPM for a few seconds then quickly lift your foot off the throttle?
With the engine off, press the brake pedal four or five times, it should get harder to press. Keep your foot hard on the brake pedal and start the engine. Does the pedal drop an inch or two further?
denephew
June 2009
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