Audi TT Power Loss: MAF/O2 Sensor Warning Signs

I experienced nearly identical symptoms with my Audi A4 1.8T (2003). The jerking during acceleration and unstable idle turned out to be a faulty fuel injector creating an incorrect air-fuel ratio. The symptoms started gradually, first unstable idle, then progressive power loss, and finally the unusual stalling. The check engine light was intermittent at first but eventually stayed on. My throttle body response was also sluggish, which initially made me think it was a simpler issue. This was definitely a serious problem that required prompt attention. The bad injector was causing a rich mixture condition, which was not only affecting performance but also risking damage to the catalytic converter. The fuel injection system needed a complete diagnostic test to identify the problematic injector. The repair involved: Full fuel system diagnostic, Removal and testing of all injectors, Replacement of the faulty injector, System reprogramming, Fuel system cleaning After repair, the engine returned to smooth operation with proper throttle response and stable idle. These symptoms should not be ignored as they can lead to more extensive engine damage if left unaddressed.

Thanks for sharing your experience with the injector issue. Mine got fixed about 6 months ago and I am still amazed at how the engine runs smoothly now. Interesting that the check engine light behavior was similar, mine also started flashing occasionally before staying on permanently. Did you remember roughly what you paid for the complete fix? My fuel injection system repair was not cheap but wondering how it compares. Also curious if you have had any other issues pop up since the repair? My intake manifold has been making some light rattling sounds lately which has me a bit concerned.

Glad I could help and great to hear your engine is running well after the fix! The complete repair cost me 515 Euro to fix the defective injection valve, which solved the mixture preparation error completely. The air-fuel ratio has been perfect since then, with no check engine lights or performance issues. The intake manifold noise you mentioned is worth getting checked though, this could potentially be unrelated to the previous injector repair. A loose or cracked manifold can mess with the engine vacuum and affect how the oxygen sensor reads the exhaust gases. Better to catch these things early before they cause bigger problems with the catalytic converter or engine performance. In my case, everything has been running great for the past year with no new issues since the injector replacement. The investment in proper diagnosis and repair was definitely worth it for the improved performance and peace of mind.

After getting that helpful advice, I finally got my car properly diagnosed and fixed. Turned out it was exactly what was described, a bad fuel injector throwing off the air-fuel ratio. The spark plugs were also pretty worn, which was making the rough running even worse. The mechanic I found did a thorough job testing the fuel injection system and showed me the faulty parts. Cost me 490 Euro total including parts and labor. The check engine light cleared up right after the repair and hasn't come back since. The engine runs so much smoother now, no more jerking or stalling. Fuel economy has improved too. Getting a proper diagnosis from a qualified shop made all the difference compared to my previous mechanic who just kept guessing at the problem. The only lingering issue is that small rattle from the intake manifold, but at least now I know it needs checking before it causes problems with the catalytic converter. Overall really glad I got a second opinion and proper fix instead of throwing more parts at it blindly.