Question1985 Cadillac Eldorado, HT4100 engine, 80,000 miles, I am the second owner, Car is like new condition.
Actions I have taken:
1.Consistently getting Code: 30- ISC Circuit.
2.New AC Delco TPS-Verified TPS set to "0"
3.Replaced the ISC Actuator with new AC Delco part.
4.All new AC Delco ignition and tune components(Maintenance)
Idle speed control actuator is ratcheting and therefore causing pedal to pulsate as well. Does it consistently when cold and will set the "Service Soon" light within 5-7 seconds. Can feel slight surge in Idle.
After vehicle warms up will not do it anymore until shut car off, than ratchets only for second or two.
Other than this the car runs and performs like new.
I suspect the Actuator is not adjusted properly, but even the mechanics today just don't know how to work on these older vehicles, they only rely on a scanner to tell them how to fix cars, just very frustrated with this.....
AnswerHello,
Your assessment on today's technicians is quite correct, but this did not happen over night and has taken over 2 decades to happen, initiating from the early 80's when about 4 years before your Caddy was built.
I have owned many Biaritz's and Sevilles with my personal favorite fun car of being an Allante. Have had many HT 4100s, 4.5s, 4.9s and 4.6 North Stars.
The problem that exists in the 1982-1993 GMs was they employed the OBD I computer system, which made exact diagnoses of a computer associated problem very difficult and challenging. These systems were not not real accurate for scanning, although OTC made scanners for them. The problem was that instead of a pin point diagnoses, you were left with a general diagnoses that could include various sensors in which a problem could cascade into being something not even being close to what the problem appeared to be. The end result was to end up chasing ghosts and needless parts changing.
In your situation, one has to go to the basics and I will give you suggestions as to what will make your diagnoses to all future problems as well, without a huge cost outlay and much more accurate results, in which you will be able to diagnose and repair this great car without having to rely on the incompetence of others that think of themselves as auto technicians with full reliance on a diagnostic scanner or they would not be able to service the vehicle. One cannot blame today's technician though, because the manufacturers have been forced because of fuel mileage mandates, and emissions concerns to end up where we are today.
In 1994, GM introduced their vehicles with the computer standard that everyone uses today, which is the OBD II (On Board Diagnostics). This system by use of a scanner can determine exactly what is wrong, what sensor, if it's a wiring issue, vacuum issue, computer issue etc. The 1993 and back GMs were not that sophisticated.
An example would be; in your vehicle, it is believed the problem is in the idle control because the motor doesn't "stem" properly, however, it is possible that the issue isn't even a problem with the stepper motor. That can be a mere symptom caused by something else.
The check engine light illuminates because a DTC (Diagnostic Trouble Code) is set causing your code 30. Whenever the check engine light comes on, the computer system is not in full loop and mileage and performance suffer. For peak efficiency, the check engine light cannot be illuminated because when it is for whatever duration it is on, the computer is not working with all associated sensors.
In order to find out exactly what the problem you have is, is that you are going to need to obtain a 1985 Cadillac Eldorado factory service manual. This can be accomplished by seeing if you can purchase one on Ebay. The manual gives you diagnostic flow charts that will guide you to a diagnoses and repair. Back in my day, this is how we fixed these problems.
You can also on Ebay find an OTC or a Snap-on scanner, with 1985 software. These are less than $100 bucks and are obviously used and will come in handy in the future for a diagnoses, not quite as general as the On board DTC you get currently.
You do not need a great amount of mechanical knowledge to use the factory manual, because it will guide you through the process of diagnoses and repair.
The manual will also assist you in many diagnoses and repairs, so you are not reliant on the new type of technician.
Good luck and let me know exactly what the issue ended up being.
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