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Running rough, lumpy idle?

Discussion in 'A4/S4 forum(B5 Chassis)' started by cossie, May 15, 2014.

  1. cossie

    cossie Member

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    Hi guys, my 2000 S4 was down on power, running rough ect so took it to my mechanic (I suspected a faulty MAF) but he couldn't find anything wrong with it! So I unplugged the MAF and the car ran perfectly, that would suggest goosed MAF. I've just installed the new MAF and now the cars power is back but the idle is lumpy as hell. It just keeps bouncing between 1-2000rpm and if you put on AC it almost dies. I've unplugged it again and it drives great but I would like this sorted as with it unplugged the dashboard lights up a few warnings. Any ideas what could be the problem and also is it ok to drive with the MAF unplugged cause I'm heading to the Highlands on Saturday via the Old Military Rd so there may be some spirited driving! Cheers.
     
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  3. cossie

    cossie Member

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    Thanks for all the help :) I've driven the car a few times now since yesterday and it's running perfectly now, wonder if it just took the ecu a wee while to recalibrate itself?? Who knows, running fine no though :)
     
  4. B5QUAT

    B5QUAT Member

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    I wouldn't run it without the MAF for any period. It's there for a reason.

    Did you buy a genuine replacement MAF or a cheapo alternative. Swapping a knackered MAF for a cheap replacement may cause you issues. Idle hunt suggests perhaps an airleak somewhere. Disconnecting the MAF is just hiding it. Check all your vac and inlet pipes and jubilee clips for leakages from airbox right to throttle housing. Get someone with diagnostic eqpt to plug in and see if any codes are coming up. That's your best bet.
     
  5. cossie

    cossie Member

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    It's a brand new genuine Bosch MAF but as I said I've left it plugged IN and drove it again and it's running perfectly now. It was just initially it was still rough but, all fine now.
     
  6. aragorn

    aragorn "Stick a V8 in it!"
    Staff Member Moderator VCDS Map User

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    probably a pile of garbage fuel trims that the ECU had learned with the duff maf, and its now fixed them :)
     

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