Results 1 to 6 of 6

LS swap tuning problem

This is a discussion on LS swap tuning problem within the Computer & Tuning forums, part of the LSx Technical Help Section category; Newbie here. I've worked in the restoration and hot rod world for many years but the vast majority of my ...

  1. #1
    Junior Member
    Join Date
    Jan 2018
    Location
    Moscow, TN.
    Posts
    3

    Silver
    1967 Chevelle

    LS swap tuning problem

    Newbie here. I've worked in the restoration and hot rod world for many years but the vast majority of my experience has been with older carbureted engines. This week a customer brought a recently purchased '67 Chevelle to me with a LS swap, supposedly a Corvette LS1. Among the long list of things that he wanted addressed was the car running cold, and a problem with the idle speed. Since I knew that engine temp can affect the engine tuning the first order of business was to correct the cold running issue. A thermostat change sorted that right out, but the idle speed issue has remained. The car has a somewhat lumpy idling camshaft but the specs are unknown.

    The idle issue presents itself like this - when the car is started cold the engine comes up to a high idle (1500 rpm) and remains there as it warms up without dropping off as the temp comes up. If you pull the car down into gear the idle drops down to about 850 rpm and it isn't straining against the convertor. Put it into neutral or park and the idle will remain at 850 rpm, unless and until you touch the throttle then it will return to 1500 and stay there unless you put it back into gear. If the engine is shut down hot and restarted it immediately comes up to the 1500 rpm idle and remains there until it is pulled into gear. I've checked the throttle cable and throttle body and there is no sticking or binding and the throttle arm returns to the stop as it should. I'm suspecting a faulty IAC but don't know how to test it and don't want to just start throwing parts at it. Any ideas on how to proceed are appreciated.

  2. #2
    Super Moderator
    pajeff02's Avatar
    Join Date
    Feb 2009
    Location
    Mansfield, PA
    Posts
    21,724

    Black & Blue
    '02 WS.6 / '07 Suburban

    If you have a scanner you can actually read all of the sensor outputs. High idle, as you probably know, is always excess air making its way into the intake. Have you verified that the throttle body and intake are not leaking and that there are no cracks in the intake? PCV system hooked up? If so, check the hoses for leaks as well. If all that checks out then I would suspect a faulty IAC or tuning issue.

  3. #3
    Junior Member
    Join Date
    Jan 2018
    Location
    Moscow, TN.
    Posts
    3

    Silver
    1967 Chevelle

    Thanks for replying. The high idle isn't consistent so I don't suspect a vacuum leak. (But I will look!) I had not located the ecu when I made the post, but I eventually did find it, bolted to the firewall BEHIND the Vintage Air unit. It appears to be a unit manufactured by Painless Performance and marketed under the name Perfect. I haven't been able to locate a connector to connect my scanner.....I tried calling them but it was late yesterday when I located the unit and they were shut down for the weekend.

  4. #4
    Super Moderator
    pajeff02's Avatar
    Join Date
    Feb 2009
    Location
    Mansfield, PA
    Posts
    21,724

    Black & Blue
    '02 WS.6 / '07 Suburban

    I would hope that they have an OBDII connector somewhere - but being aftermarket you never know. You may be able to download a manual for that controller from the company website.

  5. #5
    Senior Member Redphoenix1998's Avatar
    Join Date
    Apr 2002
    Location
    San Jose
    Age
    37
    Posts
    1,968

    Red
    1998 Pontiac Trans Am

    Here's a couple of IAC tests you can do if you have a multimeter:

    IAC Motor is a 4 wire harness
    Backprobe wire signals
    Left to right A B C D
    A= "B" (-)
    B= "B" (+)
    C= "A" (-)
    D= "A" (-)

    "B" = Coil1
    "A" = Coil2

    Check resistance with the IAC disconnected.
    Across Either Coil 1 or Coil 2 your resistance should be between 40 and 60 ohms
    if it's above or below your motor is faulty

    That should be a good starting point.
    98 WS6 M6 ASC #2647
    Forged Custom 408 w/Vortec YSi

  6. #6
    Junior Member
    Join Date
    Jan 2018
    Location
    Moscow, TN.
    Posts
    3

    Silver
    1967 Chevelle

    Thanks for the information! I've been distracted with other projects in the shop but I'll be back on this issue in a day or two. I can hear the IAC making noises like the motor is working when the key is switched on, but I'll run the tests regardless.

Thread Information

Users Browsing this Thread

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

Similar Threads

  1. Tuning for LQ4 Swap in 2000 Z28
    By My00Z28 in forum Computer & Tuning
    Replies: 16
    Last Post: 09-30-2012, 10:02 AM
  2. tuning problem??
    By robs01formula88 in forum Computer & Tuning
    Replies: 2
    Last Post: 05-28-2010, 03:54 PM
  3. Question: cam swap tuning
    By mark21742 in forum Computer & Tuning
    Replies: 13
    Last Post: 12-30-2009, 05:32 PM
  4. Question: Tuning for injector swap
    By juiced99ws6 in forum Computer & Tuning
    Replies: 8
    Last Post: 03-25-2008, 08:36 PM
  5. Tuning problem or more?
    By InsaneWs6TA in forum Computer & Tuning
    Replies: 2
    Last Post: 04-25-2007, 04:05 PM

Bookmarks

Posting Permissions

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