My Astra cuts out. But does restart why?

The REAL answer is that you have been using WRONG CHEAP OIL and now your THROTTLE BODY and IDLE AIR CONTROL VALVE As well as other engine parts have SLUDGED OVER! People that use REGULAR WAX based oil will ALSO get bad EXHAUST and CONVERTER systems and use more O2 sensors as well! >>The CURE for your ASTRA is getting ONE CAN of AMSOIL POWER FOAM and using o]it and a TOOTHBRUSH to clean the THROTTLE BODY and the IDLE AIR CONTROL VALVE! ALSO run the AMSOIL through the PCV to clean the PISTON TOPS and RINGS and VALVE HEADS! Clean BOTH SIDES of teh F body plates! Find a way to inject the AMSOIL under the INTAKE SNORKEL with engine running to clean the PISTON TOPS even BETTER!. The THROTTLE BODY also affects how the car SHIFTS! Many PRICEY cars like BMW and BENZ get diagnosed with BAD transmissions when all it is is the use of the WRONG ENGINE OIL and a DIRTY THROTTLE body! The T body controls AIR/FUEL mixture and FUEL usage in stop andf go traffic! Let ME know how things are going for you! ALSO check for ROTTEN PCV hoses as VALVOLINE and other wax based oils wil DISSOLVE rubber parts over time! People that STILL insist on using REGULAR engine oil are DOOMED to replace almost ALL the sensors and HOSES and other engine parts over time! GOOD LUCK to ou!

I have had two cars that have done this 1 was a honda accord the problem was the power load module the other a Ford escort I disconnected the battery for 24hrs reconnected and never had the problem again .

Both an easy fix one cheap the other even cheaper. Also don't hav to many keys on your key ring as that can play up on the ignition .

needs attention.

An engine needs two things to run. Fuel mixture and combustion. In a petrol engine, this is provided by an electrical spark. In diesel engines by pressure.

You have a fault with either the fuel mixture or combustion system. Due to your complete lack of detail, I cannot give a more detailed answer.

No power under load. Check for fuel pressure, clogged injectors fouled plugs and check for trouble codes. MAF sensor could be bad.

Bad ground

Could be anything without looking at it, but look for leaking vacuum pipes as these are cheap to fix. Could be a multitude of things though so you're probably better taking it to a garage.