What is fault code 050074 on astra 1.7cdti bad starting andbad idle

Your code 21 is just telling you that your left sidelight is out. The shaking and juddering is a different issue and needs a pro grade scan tool computer to see which sensor needs replacing.
21 Failure of left sidelight.

Vauxhall Astra Fault Codes - - Driving Test Tips

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Vauxhall Astra Fault Codes List ; 21, Failure of left sidelight. ; 22, Failure of right sidelight. ; 23, Failure of reversing light. ; 24, Failure of number plate ...

The service light comes on when a service is due and turned off by the service mechanic after the service , could that be the fault?.

Code 95 on your 2010 Vauxhall Astra Life points towards a fault with the airbags; in other words, your airbags require servicing. To know more about the codeson your car and what they mean, follow this link: https://www.drivingtesttips.biz/vauxhall-astra-dashboard-engine-warning-lights-meanings/fault-codes.html

is the check engine light on? if so get the fault codes out of the system for help!.the common problem is the egr valve or a clogged in butterfly/or housing contaminated

possible vacuum leak
could be a vent control hose under the dash, transmission actuator hose, brake booster leak, manifold leak
run the fault codes to find the sensor that is reporting the fault

Guessing just wastes money . have the fault codes read first and find exactly which sensor/s are causing you a problem
not all faults energize the engine light and remember the engine light also refers to problems in the transmission

You have an engine cylinder misfiring, run a fault code test with a scanner to see what cylinder is misfiring. Misfire codes look like this P0301 is cylinder number (last digit of fault code) one and so on.

could be airflow meter fault or throttle potentiometer should see check engine light flashing if either of these sensors are bad, they can effect idle and engine performance.

This is your mechanical fault light and the lack of power is the car going into limp mode to protect the engine and its components.
Have a garage run a diagnostic check to find the fault code and the fault.
Hope this helps

BAD SPARK PLUGS AND WIRES,INTAKE MANIFOLD VACUUM LEAK.STUCK OPEN EGR VALVE OR FAULTY IDLE AIR CONTROL VALVE.HAVE VECHICLE SCANNED FOR IDLE SPEED CONTROL FAULT CODE, FAULTY EGR VALVE FAULT CODE, AND BAD FUEL INJECTOR.REASON I SAY SCAN VECHICLE FIRST BECAUSE EVERYTHING COULD BE GOOD AND YOU COULD BAD GASOLINE CONTAMINATED WITH WATER.BUY A LOT OF NEW PARTS WILL ADD UP.