Audi 500SE runs intermittently

My wifes Audi 500SE starts well from cold and goes well for 5 to 20 mins, and then stops.
You can start it again and it will run OK for a shorter time, and then
stop again.
After about 3 or 4 times it wont start anymore.
When it has completely cooled of it will start again etc.
This is driving me nuts - does anybody have any ideas?
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JRvZ, Have you tried pulling engine codes? Depending on the year of the car you may be able to find errors logged in the computer. You might also check that the fuel pump is not the culprit - when the car no longer starts, if you pull an injector (and put it in an empty pop bottle), and then raise the air metering plate (accessible when removing the air filter in CIS cars), does the injector spray? Cheers! Steve

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