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348 RPM sensor question

Discussion in '348/355' started by tcannon, Jul 21, 2009.

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  1. tcannon

    tcannon Formula 3

    Feb 18, 2009
    1,763
    Norman, OK
    Full Name:
    Todd Cannon
    #26 tcannon, Aug 4, 2009
    I may have given the wrong description. It does not run rough like before where it sputtered and backfired. Now, the idle is just not constant like it was before. The other day, I could start it up and it would idle at 1000 rpm very smoothly. Now when I start it up, the idle will go from 1000 up to 1200 or 1300 and then drop back to 1000. Then it will drop down to 800 for a moment or two. Then back up to 1000. What do you think?
     
  2. No Doubt

    No Doubt Seven Time F1 World Champ

    May 21, 2005
    72,740
    Vegas+Alabama
    Full Name:
    Mr. Sideways
    #27 No Doubt, Aug 4, 2009
    Last edited: Aug 5, 2009
    Open your idle air bypass screw on each throttle body by 1 turn counter-clockwise. These have a lock nut, so hold the idle air bypass screw in place with a flatblade screwdriver while loosening the lock-nut, then use the screwdriver to turn the idle air bypass screw 1 full turn counter-clockwise, now hold the idle air bypass screw in place with the screwdriver while tightening the locknut.

    Don't honk down on the lock nut. Barely more than hand tight is fine. Repeat for both throttle bodies.

    Turn off power to battery. Turn on power to car. Start engine and let the ecus relearn by idling until the fans kick on.

    Note if idle is fixed. If so, leave it alone! If not, consider briefly pulling the vacuum line off of each fuel pressure regulator (with engine OFF!) to see if gasoline is present (indicating failure and showing that gas is going in via the vacuum plumbing, impacting idle).

    Or open the idle air bypass screws another half turn or so. If you end up raising your idle above 1,000 RPMs without solving the idle surging, then put the idle air screws back where they were and look elsewhere for the issue.
     
  3. tcannon

    tcannon Formula 3

    Feb 18, 2009
    1,763
    Norman, OK
    Full Name:
    Todd Cannon
    #28 tcannon, Aug 5, 2009
    I will report back shortly! Thanks for the help!
     
  4. tcannon

    tcannon Formula 3

    Feb 18, 2009
    1,763
    Norman, OK
    Full Name:
    Todd Cannon
    #29 tcannon, Aug 5, 2009
    Runs great! Idles smoothly again. No codes! Now, before I turned out the idle air bypass screws as you suggested, I had just removed the MAF on that bank and sprayed it with MAF cleaner. I had also just did the battery reset. I had not started it again until I completed the adjustment on the bypass screws. So now my question is this. If after a few driving sessions, it starts to do this again, does that mean it was a dirty (or faulty) MAF? Or would this mean I need to do some additional work on the bypass circuit? (cleaning?). Thanks so much for all of your help! This is such a great forum. I hope that this thread is helpful to others.



    This has been a good day for me. Earlier, I had found that the plastic piece that connects the motor to the recirc flap had sheared. I saw where Hill had a nice metal replacement. But I decided to make my own replacement in my shop. I machined some hard PVC down to the original dims of the old piece. Getting the right taper was tricky but not that bad. The hardest part was machining the square hole in the end for the motor shaft. It works great and my A/C now freezes my butt off even while it was near 100ºF today. ;) The only thing I regret is that I forgot to take a pic of my new replacement part before I installed it. Oh well. Thanks
     
  5. No Doubt

    No Doubt Seven Time F1 World Champ

    May 21, 2005
    72,740
    Vegas+Alabama
    Full Name:
    Mr. Sideways
    #30 No Doubt, Aug 5, 2009


    LOL!


    I nominate you for Stoogehood!
     
  6. tcannon

    tcannon Formula 3

    Feb 18, 2009
    1,763
    Norman, OK
    Full Name:
    Todd Cannon
    #31 tcannon, Aug 5, 2009
    Last edited: Aug 5, 2009

    Is that a good thing? LOL! :D



    PS. After doing a little research, I found out about the Stooges! I must say that it is an honor to be nominated! I hope to be able to contribute back as much as I have received already in the short time that I have been here. :bow: ;)
     
  7. tcannon

    tcannon Formula 3

    Feb 18, 2009
    1,763
    Norman, OK
    Full Name:
    Todd Cannon
    #32 tcannon, Aug 8, 2009
    Well, I started getting the 4121 code again on bank 1-4. So I swapped the MAF's and sure enough, the code switched sides. I have already had the other MAF rebuilt so I am now going to have the second one done. hopefully, that will be the end of the CEL codes for a while.
     
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