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F355 low idle

Discussion in '348/355' started by cactussed, Jan 13, 2020.

  1. cactussed

    cactussed Karting

    Mar 12, 2008
    105
    Chaps

    Got a slightly odd problem.
    Recently did some work on the car which included dropping and then refitting gearbox (broken quill shaft), dual mass flywheel regrease, new clutch bits and bobs, new thermostat.

    Put it all back together and now it struggles to idle or pick up on throttle. Runs OK once it clears the initial stutter (say, above 2k rpm).

    I don't have any OBD equipment to check any sensors but struggling to think it'd be that as none of them have been touched and I can't think which of them wold be causing the issue.

    It has all the characteristics of an air / vacuum leak (to my mind) so I replaced the idle control valve and checked all the vacuum lines I can see but still no Bueno. Its doing my head in.

    Any suggestions gratefully received.
     
  2. kenneyd

    kenneyd Formula 3
    Silver Subscribed

    Sep 30, 2014
    1,051
    NE FL
    Full Name:
    Ken
    Location?

    Lots of stuff could have been bumped, torn, unplugged doing the gear box and thermostat.
    is it throwing any codes? 2.7 or 5.2?
    Double check the plug wires, possibly unplug and re-plug each one at the coil.
    Recheck each electrical connector.
    Your most likely right about a vacuum leak. There are quite a few tubes and ports that attach into the intake plenums and throttle bodies. Its going to take some searching. good luck
     
  3. Qavion

    Qavion F1 Rookie

    Feb 20, 2015
    2,883
    Sydney
    Full Name:
    Ian Riddell
    Do you have a check engine light on? SD light? Did you need to disassemble anything above the gearbox for better access?

    Since you said "idle control valve" (singular), I guess you have a 5.2.
     
  4. phrogs

    phrogs F1 Veteran
    Rossa Subscribed

    Apr 13, 2004
    5,862
    Wyoming/Michigan
    Full Name:
    Johnny
    Any grounds missed?
     
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  5. cactussed

    cactussed Karting

    Mar 12, 2008
    105
    Nope, no lights on the dash or SD light. (its a 5.2)
    As for disassembling, not really. umplugging a few things (MAF, Idle valve, intake air temp, speed sensor) and oil lines but that's it.
    And I've reconnected the ground from gearbox to frame at the back.

    Really got me stumped.

    Pretty sure there's nothing around the thermostat area which would affect things?
     
  6. cactussed

    cactussed Karting

    Mar 12, 2008
    105
    To add, I've also checked the HT leads (its not running rough as though missing a cylinder).
     
  7. cactussed

    cactussed Karting

    Mar 12, 2008
    105
    Another thought. Would a malfunctioning / unplugged O2 sensor affect things on startup?
     
  8. yelcab

    yelcab F1 Veteran
    Consultant

    Nov 29, 2001
    9,453
    San Carlos, CA
    Full Name:
    Mitchell Le
    Plug in an OBD2 scanner and run it on live data mode while the car is running. Look for O2 sensor signals and see which one is not moving around.
    Check the vacuum lines from the engine running toward the right side and then toward the back of the car. While you are there, check the vacuum line driving the bypass valve. Check the secondary air injector lines.
    Remove the connector to the Idle Valve and inspect its pins. Do the same for the MAF connectors. Check their wires.
     
  9. zstyle

    zstyle Formula Junior
    Silver Subscribed

    Jun 28, 2007
    313
    Fountain Hills
    Full Name:
    Jon
    Please remember to let the car idle until at least one fan kicks on, especially if the battery has been disconnected with no accessories turned on.

    If the car starts rough upon initial restart, shut off quickly and restart again until the engine catches a normal idle.
     
  10. cactussed

    cactussed Karting

    Mar 12, 2008
    105
    I've ordered an ODB 3 to 16 pin adaptor and an ELM327 so will see what that shows in the coming days.
    And also aware of the ECU learning cycle but this isn't normal.

    Going to check connections, spray some carb cleaner around and see what happens ahead of the OBD turning up.
     
  11. johnk...

    johnk... F1 Veteran
    Owner

    Jun 11, 2004
    7,576
    New England/FL

    No learning cycle on a 5.2 car. Just start without depressing the accelerator with all accessories off.
     
  12. cactussed

    cactussed Karting

    Mar 12, 2008
    105
    Well as usual, it turns out the problem rests with the one holding the spanner (i.e., me)!
    Started and went around with carb cleaner and all tight as a drum.
    So, decided to pull HT leads and the RH bank was sparking but no change to running when pulled. I therefore reasoned I had spark but no fuel.

    thinking back.....

    I had to pull the fuel lines that side to change the thermostat...

    Sure enough, I'd connected them back into the block back to front, so the RHS bank wasn't getting fuel.

    Switched them around and presto!,runs like charm.

    Lesson learned - check and re-check everything!
     
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  13. yelcab

    yelcab F1 Veteran
    Consultant

    Nov 29, 2001
    9,453
    San Carlos, CA
    Full Name:
    Mitchell Le
    This is why I work on my own cars. I know where the stupid bastard is everytime.
     

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