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Q:

engine starts but stall immediately. fault codes P0171,P0725,P1857 and P1850 on 1999 Volkswagen Beetle

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have manual but these particular codes are not listed. I have replaced the fuel filter,fuel pump relay switch and two vacumm lines still have same problem even after reseting computer.
(2) Answers
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P0171 is a lean air mixture code and P0725 is a engine speed sensor fault. I do not see the other codes in fault code list. You may be getting some bogus codes depending the scanner that gets the code for you. P codes are generic but VW uses codes like 5 digit numbers. Might try clearing codes and retry starting and see what comes back. VW has had a history of mass air sensor failures and the P0171 would relate to that.
Your spark plugs must be set perfect. If not the vehicle will keep stalling. Check your spark plug wires also they wear out after time.