Engine braking

Discussion in 'General Tech' started by Tommy92, Feb 7, 2014.

  1. Tommy92

    Tommy92 Active Member

    Messages:
    889
    Likes Received:
    24
    Joined:
    Sep 30, 2011
    Location:
    Los Angeles, CA
    I noticed whenever I downshift or let off the gas, it does not slow down the car. The rpm doesn't slow down as if I kept my foot on the pedal when in actuality its off the pedal. If I downshift without rev-matching the car does slow down for a little then the rpm stops dropping and stays constant again. When I had my Mach 1, I would use engine braking and I want to find a way to get it back. I don't know if this has to do with anything, but when I put my car into neutral or push the clutch in the RPM hangs above 1300 rpm until I come to a full stop. Also, between shifts when I push the clutch in the RPM goes up slightly (~100 rpm).

    I had a problem with my IAC before giving me rough idle but I got a new one and it went away so I don't know if that's the problem. Its not from Motorcraft though.
     
  2. ryclef331

    ryclef331 Well-Known Member

    Messages:
    2,913
    Likes Received:
    9
    Joined:
    Jan 20, 2006
    Your two problems are absolutely related. I would replace the IAC with a motorcraft part first and start there. You should also double check that your TPS is functioning properly. You can google how to test tps voltage and it will come up with a million search results. That should get you patched up. Your IAC isn't closing all the way due either to it malfunctioning and sticking OR something is telling it to remain open (TPS).
     
  3. Tommy92

    Tommy92 Active Member

    Messages:
    889
    Likes Received:
    24
    Joined:
    Sep 30, 2011
    Location:
    Los Angeles, CA
    I see, I'll pick up a new Motorcraft IAC tomorrow and see if that helps. Thanks!
     
  4. CC'S95GT

    CC'S95GT Legend

    Messages:
    10,738
    Likes Received:
    171
    Joined:
    Apr 19, 2008
    Location:
    Hampton ,Ga.
    My hanging idle was due to a dead spot in the TPS.
     
  5. RichV

    RichV Well-Known Member

    Messages:
    4,227
    Likes Received:
    247
    Joined:
    May 6, 2012
    Location:
    CO
    I thought ford put that in their ECU strategy. Can't remember the term, but in a nutshell it was a hanging idle on the manual cars.
     
  6. ryclef331

    ryclef331 Well-Known Member

    Messages:
    2,913
    Likes Received:
    9
    Joined:
    Jan 20, 2006
    True. Its called the "dashpot funtction" and it allows a slight "hang" but its merely there to assist with smother shifting with the stick cars however...it shouldn't "hang." to the extent he and many others describe. If its idling high at stop lights, slow to return to a normal idle, and acting as if cruise control is on, its a malfunction.
     
  7. RichV

    RichV Well-Known Member

    Messages:
    4,227
    Likes Received:
    247
    Joined:
    May 6, 2012
    Location:
    CO
    Yea, mine will idle high until I come to a stop.


    Even if I clutch at 60mph, it will still idle a little higher.
     
  8. Tommy92

    Tommy92 Active Member

    Messages:
    889
    Likes Received:
    24
    Joined:
    Sep 30, 2011
    Location:
    Los Angeles, CA
    Did you also experience no engine braking/cruise control symptoms?
     
  9. CC'S95GT

    CC'S95GT Legend

    Messages:
    10,738
    Likes Received:
    171
    Joined:
    Apr 19, 2008
    Location:
    Hampton ,Ga.
    Sometimes. I have 4:10 gears so my rpm's run higher. But if I put it in neutral and coasted to a stop the rpm's would hang about 1000-1200 rpm's. Sometimes it would come down slowlyon it's own, sometimes bliping the throttle would bring it down , sometime nothing would.
    I pulled it off and ran a restistance ck on it and found a dead spot near the idle position. You can also ck it installed by back pining the connector.
    If using a digital volt/ohm meter make sure you move the throttle very slowly or you may miss the dead spot. Once you find something repeat the test amd make sure the dead spot is in the same location every time,
     
  10. Tommy92

    Tommy92 Active Member

    Messages:
    889
    Likes Received:
    24
    Joined:
    Sep 30, 2011
    Location:
    Los Angeles, CA
    I have warranty on my IAC so I'll exchange that with a Motorcraft IAC and if that doesn't work I'll take a look at the TPS. Thanks!
     
  11. Tommy92

    Tommy92 Active Member

    Messages:
    889
    Likes Received:
    24
    Joined:
    Sep 30, 2011
    Location:
    Los Angeles, CA
    Case closed. I picked up a Motorcraft IAC and installed it today. No more rpm rushing up between shifts and comes down smoothly when I come to a stop. Also got my engine braking back. Thanks everyone!