Page 1 of 2 12 LastLast
Results 1 to 15 of 19

Thread: Have to brake to drive below 35MPH

  1. #1
    Join Date
    Apr 2020
    Posts
    11

    Question Have to brake to drive below 35MPH

    2003 idles at 850-900 rpm but cannot drive below 35 without braking to slow down

  2. #2
    Join Date
    Dec 2011
    Location
    New Haven, Ct
    Posts
    964

    Default

    Good afternoon,

    I am a bit confused by your post. Can you clarify what you are experiencing and what you believe is abnormal? Are you an automatic or a standard? What modifications do you have on your vehicle?

    Also, your idle is WAY TOO HIGH.

    Allthebest, Paul
    GM World Class Certified Service Technician.
    Like us on Facebook: www.facebook.com/corvettemechanic
    Twitter: www.twitter.com/GMvettemechanic

  3. #3
    Join Date
    Apr 2020
    Posts
    11

    Default

    Quote Originally Posted by c4c5specialist View Post
    Good afternoon,

    I am a bit confused by your post. Can you clarify what you are experiencing and what you believe is abnormal? Are you an automatic or a standard? What modifications do you have on your vehicle?

    Also, your idle is WAY TOO HIGH.

    Allthebest, Paul
    Sorry...Automatic trans in neutral idles @ 850 when in drive will run at 1100 rpm and 35 mph with foot off gas
    No alterations I am aware of....purchased used

  4. #4
    Join Date
    Dec 2011
    Location
    New Haven, Ct
    Posts
    964

    Default

    HI there,

    I am assuming that there is no check engine light, which would indicate that the computer is not seeing an issue.

    #1, make certain that there is not a floor mat or something of that holding the gas pedal from returning to its stop.

    #2, if there is nothing there, turn the vehicle off, and check to make sure that there is nothing under the hood that might be interfering with the throttle blade.

    Please keep us posted, Paul
    GM World Class Certified Service Technician.
    Like us on Facebook: www.facebook.com/corvettemechanic
    Twitter: www.twitter.com/GMvettemechanic

  5. #5
    Join Date
    Apr 2020
    Posts
    11

    Default

    Thank you Paul, I will check again but I don't think there is anything in the cockpit.
    How do I check the throttle blade?
    I have noticed if the A/C is running it runs 100 rpm or so faster will in drive and no load sometimes 1500 r's

  6. #6
    Join Date
    Dec 2011
    Location
    New Haven, Ct
    Posts
    964

    Default

    HI there,

    Remove the intake system duct between the Mass Air flow Sensor and the throttle body.

    Then, with the ENGINE OFF, disconnect the throttle body connector and then see if the throttle body blade inside moves freely. It is spring loaded to slightly open.

    But you should be able to move the throttle blade with your finger fully OPEN and fully closed.

    Visually check to make certain that all hoses are connected and there are no vacuum leaks also while you are inspecting the throttle body.

    Allthebest, Paul
    GM World Class Certified Service Technician.
    Like us on Facebook: www.facebook.com/corvettemechanic
    Twitter: www.twitter.com/GMvettemechanic

  7. #7
    Join Date
    Apr 2020
    Posts
    11

    Default

    Thank you,
    Everything appears to be OK
    I will probably take it to a Corvette dealer. I had it to a very good independent but they couldn't find anything. They said the 850 no load idle is correct.
    With the A/C on in drive it will slowly (no accelerator) get up to 35 I brake down to 20 and within a minute or so it is back to 35+-
    With A/C off it will go to about 30 with A/C on and no load (neutral) idles at about 1500, under load (drive) about 1050-1100

  8. #8
    Join Date
    Dec 2011
    Location
    Washington State
    Posts
    585

    Default

    Quote Originally Posted by 1953CE View Post
    Thank you,
    Everything appears to be OK
    I will probably take it to a Corvette dealer. I had it to a very good independent but they couldn't find anything. They said the 850 no load idle is correct.
    With the A/C on in drive it will slowly (no accelerator) get up to 35 I brake down to 20 and within a minute or so it is back to 35+-
    With A/C off it will go to about 30 with A/C on and no load (neutral) idles at about 1500, under load (drive) about 1050-1100
    Check your complete PCV valve hose that attaches to the throttle body and make sure that it is not soft, collapsed, or has a hole in it.
    20+ years ASE and Honda Master Tech

    1998 black 6 spd convertible

  9. #9
    Join Date
    Apr 2020
    Posts
    11

    Default

    Quote Originally Posted by LLC5 View Post
    Check your complete PCV valve hose that attaches to the throttle body and make sure that it is not soft, collapsed, or has a hole in it.
    Hose and connections appear to be in good order

  10. #10
    Join Date
    Dec 2011
    Location
    Washington State
    Posts
    585

    Default

    Quote Originally Posted by 1953CE View Post
    Hose and connections appear to be in good order

    If there are no external vacuum leaks, then make sure that your throttle blade is closing fully as stated previuosly by c4c5, carbon build up is one reason it may not be closing fully.

    Is there a check engine light on, or any codes in the DIC?
    20+ years ASE and Honda Master Tech

    1998 black 6 spd convertible

  11. #11
    Join Date
    Apr 2020
    Posts
    11

    Default

    Quote Originally Posted by LLC5 View Post
    If there are no external vacuum leaks, then make sure that your throttle blade is closing fully as stated previuosly by c4c5, carbon build up is one reason it may not be closing fully.

    Is there a check engine light on, or any codes in the DIC?
    No Codes or light
    Will check again but bear in mind she idles no load at 850-900 which they tell me is about right
    It just acts weird while in drive 1100

    Thanks to all for your suggestions , I appreciate it

  12. #12
    Join Date
    Dec 2011
    Location
    Washington State
    Posts
    585

    Default

    Quote Originally Posted by 1953CE View Post
    No Codes or light
    Will check again but bear in mind she idles no load at 850-900 which they tell me is about right
    It just acts weird while in drive 1100

    Thanks to all for your suggestions , I appreciate it

    The 850-900 is too high for OEM engine and tune. It should be 600-650 rpms.
    20+ years ASE and Honda Master Tech

    1998 black 6 spd convertible

  13. #13
    Join Date
    Apr 2020
    Posts
    11

    Default

    How do I lower the idle speed (I'm an old carb guy)

  14. #14
    Join Date
    Dec 2011
    Location
    New Haven, Ct
    Posts
    964

    Default

    HI there,

    NO, Larry is absolutely correct 600-700 rpm is accurate.

    The issue is that it is all computer controlled. That is why we suspect a vacuum leak because that allows extra air into the engine, and therefore, raises your idle speed. An effective check of the MAF sensor readings can tell you if you have a vacuum leak or not.

    Have someone do an accurate scan of all the data to confirm a vacuum leak or simply do a smoke test of the entire induction system.

    Allthebest, and please keep us posted, Paul
    GM World Class Certified Service Technician.
    Like us on Facebook: www.facebook.com/corvettemechanic
    Twitter: www.twitter.com/GMvettemechanic

  15. #15
    Join Date
    Apr 2020
    Posts
    11

    Default

    Thanks to all.....to the dealer she will go

    Great site...super people

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •