Having a bolt snap off while you’re undoing it is a royal pain and can bring take the car off the road if it’s a critical fastener. You’re probably best off visiting a mechanical engineering shop (or good workshop) who will have the tools necessary to remove the broken chunk of bolt still lodged in the car.

Techniques vary according to how much bolt is still showing, access to it and even what it’s made from. In some cases, the engineer will use what’s called a bolt-extractor kit which screws into the broken bolt and extracts it without damaging the existing threads. If you’re lucky there will still be enough of the broken bolt exposed to allow the use of vice-grips to remove it. Sometimes a small section of new metal can be welded to the broken stud or bolt to give purchase and in extreme cases there’s even a process called spark eroding which is more expensive but can really save the day. The last resort is usually drilling the broken bolt out as this can destroy the threads in the part, requiring even more work to ultimately replace the fastener. In each case, penetrating fluid and/or the application of heat will be the first step to try to free or loosen the broken fastener before trying to extract it.

It sounds like you’re dealing with a fuel-air mixture issue when the engine is started from dead cold. If the mixture is too rich – which would be my suspicion – then black smoke is often a consequence.

A coolant temperature sensor should be telling the engine’s on-board computer what the temperature of the engine is, so that the computer can then tell the injectors how much fuel to inject into each cylinder. A dud sensor can cause the computer to inject too much fuel, and there’s the source of your black smoke. As the engine warms up, the sensor starts sending the correct signal to the computer and the smoke stops.

Of course, it’s not always that simple and you could also be looking at a blocked air filter, a blockage in the air intake system, worn fuel injectors and plenty more. Even a stuck or jammed thermostat can cause an engine to run poorly and blow black smoke if it can’t maintain the engine at the correct temperature. Old or stale fuel in the tank can also cause these symptoms. The fact that your car is not showing any fault codes suggests that perhaps you’re looking at one of these old-school problems.

It is low for the discs to require machining, but the Astra is a European car and they tend to have a higher brake wear rate than cars from Asia.

Have the dealer/mechanic show you the measurements of thickness they took that demonstrates the need. With brakes being considered a wear and tear item it’s a long shot if you’re thinking Holden might come to the party with the cost of the machining.