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Cold start issues? Maybe it;s your O2 sensor.

eddyg Mar 21, 2006

  1. eddyg

    eddyg Member


    For the past year my S3 has been having a minor cold start issue. Upon the first start every morning it would cough and splutter for 30secs and then run fine.

    I tried and tried to find the cause, and gave up due to escalating mechanic and diagnostic bills. There was no obvious cause, and it only happened for 30secs each day - so it wasn't worth pursuing.

    I went for a 1000km blat over the weekend to clear the cobwebs when towards the end at 110km/h the EPC and traction control lights lit and I lost all power. I coasted to a halt. The engine was still running, but sounded like a tractor and wasn't making any power. So I restarted the engine - and it worked fine again.

    Since that time all my cold start issues have cleared up.

    So I took the car in to my mechanic to check the fault codes, and sure enough it now had some, finally!

    6 codes were thrown, 4 of them unknown ones. But two of them were for the O2 sensor and the O2 sensor heater.

    The O2 sensor had died and the car upon restart had assigned the last known good reading and kept it at that. Which is why my cold start issues had gone. I've ordered a replacement.

    So - if you get any cold start hiccups then suspect your O2 sensor. Get a VAGCOM or something to monitor it during startup and see what silliness it is reporting.

    Hopefully this is also going to clear up my part throttle hesitations in 1st gear. But I doubt whether it will fix my buggered 3rd gear synchros.

    Cheers, Ed.

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