How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Roman Your Own Question
Roman, Technician
Category: Audi
Satisfied Customers: 556
Experience:  over 20 years vw audi and porsche technical repair
Type Your Audi Question Here...
Roman is online now
A new question is answered every 9 seconds

Hi, my daughter has an 2004 Audi A4 Cabriolet 1.8 Turbo. After it runs for 45 minutes or s

This answer was rated:

Hi, my daughter has an 2004 Audi A4 Cabriolet 1.8 Turbo. After it runs for 45 minutes or so it starts to hesistate really bad with any form of acceleration. Check engine light is on, fuel filter and spark plugs have just been replaced after the problem started. I do not have the exact codes but the engine is running lean
Hello ,
Here to answer automotive questions and make you feel comfortable and become familiar with your product
Having the faults will narrow it way down. There could be many variables. Get the faults and list them for me to evaluate. You can go to pepboys,autozone, or aamco for a free check.
Let me know and we will find out together how to fix the problem.
Customer: replied 3 years ago.

Hi Roman,


Thanks for your reply. I will get the fault codes tomorrow and email them to you. Thanks for your help.



just list them when you are ready
Customer: replied 3 years ago.
Hey Roman, the only code that I got was P0171 system too lean, bank 1
Explanation is low fuel pressure or volume
Possible causes Faulty ho2 sensor, large vacuum leak or faulty MAF sensor.

What do u think?

First check for vacuum leaks. If you dont find any replace the maf. Check around the combi valves for leaks in the vacuum lines.
Roman and 2 other Audi Specialists are ready to help you
Customer: replied 3 years ago.

Hey Roman,


Finally had a new MAF sensor delivered and I just installed it. The car now runs about 90 minutes versus 45 before it starts hesitating and chugging. I cannot hear or see any vacuum leaks. I have already replaced the air filter, fuel filter and plugs. Idea's? Still getting the P0171 code.



you can check the secondary air system for leaks. In the back of the engine there is a silver metal valve called a combi valve. Check and replace any leaking vacuum lines. Follow the rubber lines under the intake manifold on the ds. There maybe some broken lines under there. Check the oil dipstick and oil cap is not broken or leaking.

Let me know if you find anything there. I will recommend some others if you dibs nothing. I think its Better to go step by step so we are Bitch on the same page together.
Customer: replied 3 years ago.
Roman, should there be suction on the oil dipstick when the car is running. There is none on the Audi
The combustion wll create vacuum and will be very evident on newer model year audis. Some of the new engines will not run or run very rough if the dipstick is broken or missing.

Yours will have very little vacuum but will need a good seal from a proper installed dipstick in the funnel. Just make sure it fits properly to eliminate leaks.

Do you find any broken vacuum lines under the intake, on that side. Look for any that are going to solenoids and the combi valve In back of the head.

On the intake you will see a black hose leading down between the engine and radiAtor to a black valve. This valve sometimes leaks internally. It is for the turbo. Also there is a turbo diverter valve which cam leak internally

This post has some photos of it and the location.

Related Audi Questions