Misfire/Stumble when letting off gas pedal/maintaining steady

Discussion in 'GMC Truck Forum' started by Matt Kuhar, Jun 22, 2015.

  1. Matt Kuhar

    Matt Kuhar Full Member

    Joined:
    Jul 26, 2012
    Messages:
    716
    Likes Received:
    360
    Trophy Points:
    63
    Location:
    New Haven County CT
    hey guys,

    im still having issues with my truck misfiring/stumbling at steady speed, does not matter cold or hot same thing happens. i can run at approx. 75% pedal all the way to WOT and it runs like a champ. its everything in between that has issues but only if im easy on pedal, if the motor is under load itll run fairly decent, and ALWAYS runs great at 75% or more throttle. im thinking some kind of sensor? i should mention that my exhaust is pretty much non-existent right now as it was clogged but my mech cut the cat open so it would run, but i had this issue prior to that being done as well. ripping my hair out with this problem.

    List of work in last year to 1.5 years:

    Crank Sensor
    Cam Sensor
    Distributor
    Cap & Rotor (2 times)
    Speed Sensor
    MAF
    CTS
    New Injectors (FPR with them)
    Fuel Pump
    Fuel Filter
    Ignition Coil
    Ignition Control Module
    Spark Plugs (AC Delco)
    Spark Plug Wires
    MAP (2 Times)



    Compression was tested at the shop, and he said it was within tolerance but i didnt ask for the specific PSI from each cylinder :/


    Sensors i havent done, Yet...


    IACV
    TPS

    i think those are the only 2 sensors i have not touched yet.


    any ideas???
     
  2. MrMarty51

    MrMarty51 Full Member

    Joined:
    Aug 7, 2013
    Messages:
    7,404
    Likes Received:
    10,150
    Trophy Points:
    113
    Gender:
    Male
    TPS, first guess.
     
    2 people like this.
  3. Matt Kuhar

    Matt Kuhar Full Member

    Joined:
    Jul 26, 2012
    Messages:
    716
    Likes Received:
    360
    Trophy Points:
    63
    Location:
    New Haven County CT
    i should also mention it randomly surges at idle sometimes to 2,000 RPM give or take. thats not able to be done on demand, usually happens on first start of the day if its gonna happen. would that also point to the TPS?
     
    3 people like this.
  4. MrMarty51

    MrMarty51 Full Member

    Joined:
    Aug 7, 2013
    Messages:
    7,404
    Likes Received:
    10,150
    Trophy Points:
    113
    Gender:
    Male
    HHHMMMmmm, that might be caused from, a vacuum leak other than the IAC, something controlled with the temps. or, it could be the IAC is sticking or, it could be the TPS. Also, put a multimeter on the CTS and see how it relates, in coordination with the engine temps. Use one of them infrared digital thermometer thingamabobs, measure the temps right next to the CTS.
     
    1 person likes this.
  5. chevychase

    chevychase Semi-Admin
    Staff Member

    Joined:
    Oct 15, 2010
    Messages:
    22,489
    Likes Received:
    13,327
    Trophy Points:
    113
    Occupation:
    SELF EMPLOYED
    Location:
    truck forum .org
    Sounds maf related to me..make sure air intake/plenum is sealed tight in maf stream.
     
    3 people like this.

Share This Page