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A4 bad starting, MAF sensor?

  • #1
    Registered Users Posts: 919 ✭✭✭ MrCostington


    Hi, you may (perhaps) remember I posted a few months back having failed the NCT on emissions ('02 A4 B6, ALZ engine code I think). Plugs badly fouled, then bad starting and very bad running. It somehow righted itself after a plug change and passed the NCT comfortably.

    The bad starting has been back again, just when stone cold, it will fire, cough, splutter and then die. It does this on about 4 to 6 tries before it starts, then runs fine, and will start fine after a few minutes warmup. See video below (did not capture the sound too well unfortunately but shows revs). There is no codes or light.

    In addition to posting here I also posted on a VAG forum and they suggested the coolant temp sensor, which I tried as it was just 12 quid. No change. They also suggested the MAF sensor and crankshaft position sensor.

    I'm looking at the MAF now, it's a 4 pin type, and I got the following resistance readings (unplugged & pin numbers as written on the plug/harness) :
    • 1,2 - 3.7 K ohm
    • 1,3 - open circuit
    • 1,4 - 6.3 K ohm
    • 2,3 - open circuit
    • 2,4 - 2.6 K ohm
    • 3,4 - open circuit

    So, it would appear that pin 3 is not connected to anything. There are 4 wires going into the plug. If the MAF just has simple resistance wires, then I found a problem, however, if there is electronics in it, these could be valid values in an inactive state. I understand there are 3 types of MAF, simple resistance, slow frequency out and high frequency out. The latter two must have electronics in them?

    To experiment, I unplugged the connection the last few days, and the car is starting on the button now! It did throw a P0102 and PP0113 though. So, with the MAF connected, no errors and bad starting, disconnected, errors and good starting and running!

    Any thoughts, as the MAF is at least 130 quid.



Comments



  • If disconnecting the MAF improved things then it could be that.
    If it is the resistance/wire type then perhaps try spraying airflow sensor cleaner.

    I recently had a similar problem on another car. Turned out to be the fuel filter. Only about €10-€12.

    When was the last time it was changed?




  • Hi, thanks, just seen your reply.

    Is electrical contact cleaner the same thing, I came across someone saying it is on YT. But, if my pin 3 really is open circuit, I don't see how that might help. Worth a try though.

    Re the filter, I thought of that. But, since it runs OK once started at high revs/load, when fuel flow is high, would that not discount a blockage there? No idea when last changed, not in my ownership, 3 or 4 years.




  • Hi, thanks, just seen your reply.

    Is electrical contact cleaner the same thing, I came across someone saying it is on YT. But, if my pin 3 really is open circuit, I don't see how that might help. Worth a try though.

    Re the filter, I thought of that. But, since it runs OK once started at high revs/load, when fuel flow is high, would that not discount a blockage there? No idea when last changed, not in my ownership, 3 or 4 years.

    Electrical contact cleaner shouldn't do any damage to the sensor, but I'd use a dedicated maf sensor cleaner just because how sensitive they are.




  • Do not use electrical contact cleaner because it is not designed for such a purpose. MAF sensor cleaner does not leave any residue and evaporates quickly. I completely understand why people like to use electrical contact cleaner. It is cheap and available everywhere. MAF sensor cleaner cost double the price and most of the Irish shops does not have it on the stock. I typically order it from Germany when needed. It is bit off the topic but other very important thing what Irish shops does not have is distilled water. Do not ever use de-ionized water on your car cooling system.

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