2004 Audi A4 with 0171 0300 0301 0302 0303 0304

2004 Audi A4. No prior problems at all. Yesterday after work my light came on. Car has 76,000. Codes are

0171- system too lean, cylinder #1 denotes bank 1
explanation : low fuel pressure or volume
probable causes: faulty H02 sensor, vacuum leak, MAF

0300- random cylinder misfire
explanation : lean air/fuel ratio
prob causes: ign system misfire, fuel injector fault, mechanical condition

0301-0304- each cylinder misfires
explanation: vacuum leak on engine
prob causes: ign system fault, fuel inj fault, mechanical condition

If they give me an explanation of Vacuum leak does that mean there is definitely a leak? I don't believe ALL spark plugs or ALL coil packs are bad, think the misfires are caused by whatever set off 0171? What is the best way to check each prob cause - I can't afford to guess and replace both O2 sensors, and MAF, and whats the best way to find a vacuum leak if I can't hear it?

Thanks in advance

Check/clean MAF.

Check fuel pressure (with pressure guage).

Visually inspect all vacuum lines (including the intake nozzle and PCV system) for cracks, holes, disconnected, mis-routed.

Check intake manifold gaskets for vacuum leaks as well with propane while watching fuel trims.

Good luck and keep us posted.

Thanks for the fast reply!

OK I think I found a vacuum leak (I'm a 25 yr old girl, not a mechanic )

I did the stethoscope trick and listened for the leak. Then I sprayed the hose with carb cleaner and it raised the idle. I'm not sure if it's enough to cause my problems though... I attached a couple pics, the hose has a white arrow pointing to it but the leak is at the end about 2 inches down near the red arrow.

If spraying carb cleaner notably affected the idle, chances are you found the leak.

Replace the hose and you should be good to go.

Nice work!