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86 T-Bird - Most likely cause of failing cold idle?

My mom's 86 T-Bird with 3.8 CFI has just lost its cold idle ability. I've only done a cursory visual inspection for obvious signs such as vacuum leaks, loose/disconnected connectors, etc. Before I begin a more in-depth inspection of settings and CFI components I was hoping to get some "most likely" pointers from those familiar with this model.

When the vehicle is started cold it exhibits no cold idle-up which it normally would even on the warmest of days. The current temps here in the morning are ranging between 30 and 50 degrees. Once the engine is at or near operating temps it idles and runs fine.

Btw, I would like to thank those that gave advice on heater core replacement in this same vehicle. Using the practical knowledge and webpage pointers given by many I was able to complete the job in "under" 3 hours...doing it properly! You people were invaluable!

Best Regards, Ej

Reply to
Mark
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Quick update...

Guess I should have done this prior to posting...just performed a KOEO test and produced codes 31 (PFE) and 63 (TPS). Cleared codes and await duplication upon retest, right now all I get is 11 and 111 (sys ok). Will re-check after cold-start tomorrow.

Ej

Reply to
Mark

Most likely this:

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Reply to
Sharon K.Cooke

A CFI (central fuel injection) engine does not have an IAC, because fuel is injected into the throttle body, not the manifold. There were several idle control mechanisms on the 3.8CFI - the one I am familiar with is the ISC - a servo motor that pushes the throttle stop up and down. If that's what you have, you should hear (and see) the servo retracting when you run KOEO. You should also test the contact switch at the tip - press on it after the stored code have finished and the computer is in 'output' mode. You should see the light turn on and off with each pressing.

Will need to look up code 63. If it's TPS out of range, you should certainly fix it first. When done, run KOER (make sure to warm the engine up first and 'goose' the throttle when you get the blink during the test).

Reply to
Happy Traveler

Thanks for the reply Happy Traveler. You were spot on!

Even though I checked it while still warm I was able to note the following:

  1. Depressing the ISC switch after code cycling produced no LED illumination.
  2. There was no extension/retraction of ISC motor during any inputs or operations.
  3. With key in RUN position a judicious tap on the ISC produced extension!

Being the tightwad I am I removed, overhauled, and reinstalled the unit and all works well now. I worked on Mitsu's many a year and got use to doing a similar repair in an effort to save the clients over $300...to the chagrin of the parts dept. ;-)

Many thanks for zeroing in on the suspect. I like to spend as little time as possible working on vehicles when the weather is cold outside (no garage at her house).

Regards, Ej

Reply to
Mark

Thanks Sharon. Yup! Same thing...just different. ;-)

Appreciate the support.

Ej

Reply to
Mark

Glad you fixed it. Forgot to mention that the ISC is not only for idling, but it also acts as a 'dashpot', chasing the throttle and preventing it from sudden closing. That, I believe is the main reason for the contact switch. Make sure it works...

Reply to
Happy Traveler

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