Jim Grant's Tech Tips
'91 Buick Park Avenue, Idles at 80MPH
Q: I just traded for a '91 Buick Park Avenue. It runs great; just excessively fast! Starts with a high idle and stays that way 92% of the time. A computer test said "faulty cruise-control". The mechanic said that couldn't be it. Air filter & butterfly are clean. Many mechanics have given different diagnosis. Please help if you can.
- Melissa A.
A: When the scan tool was connected to the computer the technician should have looked at other information as well. By using the information displayed by the scan tool the technician would be able to determine if there was a mechanical or computer command problem. Mechanical problems like vacuum leaks or failing idle air control motors can result in a high idle condition. By viewing the computer data one can determine if the computer is commanding the high idle or if it is trying to reduce the idle speed. If the computer is trying to reduce the idle speed, it is likely, that there is a mechanical problem that its trying to compensate for. By viewing the correct data a logical diagnostic path can be developed. If the computer data shows the computer intentionally commanding a higher idle speed then the technician should be looking for input information to the computer that is out of range. If Im not mistaken, the throttle position sensor voltage is critical, it only has to be out of range by a 10th or two of a volt (thats right a 10th of a volt) can cause idle control problems. Anybody can plug into a computer and get codes with a scan tool or code reader. Real information used by a real technician should provide the solution to your high idle problem.