Expert: autohelp - 12/4/2008

Question
QUESTION: I have a 1986 Deville with the HT4100.  The idle speed goes intermittently fast usually at start up. When it does, the ISC won't retract.  I have checked the on board diagnostics, set the TPS to 0.5V, and the ISC to approximately .030".  I even bench tested the ISC and saw no problems.  I am frequently getting either a code 26 or 27 (or both) sometimes just when turning the key on (without starting the engine) At this point I am wondering if the ECM is causing my problems by not supplying the reverse voltage to retract the ISC when needed.  Thanks.

ANSWER: You can extend and retract the ISC while it is still on the engine via the climate control panel to see if it operates smoothly without any clicking noises internally or at full extension.

If you are mechanicaly inclined or know of someone who is, You will need a DIGITAL MULTIMETER, Simple electrical schematics, Test procedures and picture locations of the components within the system that is causing you problems of which can't be done on this website which only allows one picture. I do not have a website so you will have to e-mail: onlineautohelp@msn.com in order to obtain the information.


---------- FOLLOW-UP ----------

QUESTION: I have used the climate control panel diagnostics (9.6) to test the ISC extension and retraction.  What I have found is it will only extend and not retract under this test with constant clicking as it is trying to continue to extend beyond its limit.

Answer
You need to replace the ISC motor and make the base idle speed, TPS and ignition timing adjustments BEFORE adjusting the new ISC motor.

If you are mechanicaly inclined or know of someone who is, You will need a DIGITAL MULTIMETER, Simple electrical schematics, Test procedures and picture locations of the components within the system that is causing you problems of which can't be done on this website which only allows one picture. I do not have a website so you will have to e-mail: onlineautohelp@msn.com in order to obtain the information.