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1984 Eldorado
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42 Posts
Discussion Starter #1
Hello to all. I have a 1984 Eldorado with the good ol' HT4100 engine. It runs smooth but the idle is way too high. Don't have a tach so I'm guessing somewhere around 1000 to 1200 rpm warm. Obviously it's higher when cold. I found some old posts on this topic but having read through them I am seriously afraid to try and adjust it. It seems there is an ISC, booster motor, sensors, etc. which need to be synched and working in order to get the idle down to around 600/800 rpm. Am I correct? The car is now in Germany so I can't go down to O'Reilly's and get new parts. I read about "Idle learn" which sounds like a good place to start but don't know where to find it. Is it a website or something in the shop manual? I just want to gather info to access the complexity before I go on to getting under the hood. Any suggestions or help would be appreciated.
 

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1985 eldorado biarritz convertible
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151 Posts
i had the same exact issue recently on my 85. i went through the relearn / adjustment procedure as per manual with the original ISC in place. i didnt get a positive result. i then replaced the ISC with a unit from rockauto , installed , adjusted the plunger accordingly , adjusted the TPS as well , went through the relearn procedure as per manual , and now she is good as new. i checked all the vacuum hoses as well for any possible leaks as that may cause high idle as well.
 

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1984 Eldorado
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42 Posts
Discussion Starter #4
Hello Submariner. Yeah, that's where I got the first part of the complexity. I hate to say it, but I remember on my '67 Chevy idle was adjusted via a linkage screw which amounted to "screw in higher; screw out lower" deal. So all these components for as simple as idle speed seems daunting. And I really don't want to get the vacuum involved either. Sounds great but this gets realhard on older cars. Vacuum hoses can dry rot or expand and come off. Way too complicated. But, I can't re-design the car, so I will persevere. Any tips would be appreciated.ly
 

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1926 Model T street rod, 2000 Jaguar XJ8, 1999 Corvette.
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6,737 Posts
To set idle speed. Remove air filter and lay over to the side, vacuum hose left connected to it. Now locate the idle speed motor.( ISC) With the engine running, lift the throttle lever to clear the idle motor shaft. Once clear, press firmly on the shaft with your other hand, keeping constant pressure on it till it fully retracts. Once retracted, QUICKLY remove the electrical connector to it. Now let the throttle lever come back to rest. It should idle at about 400 RPM. Shut off the engine. Measure the clearance between the throttle lever and idle motor shaft. It should be 60 thousands measured with a feeler gauge. If no clearance, rotate the shaft in with a pair of pliers to get that clearance. Now, reconnect the electrical connector. Restart the engine. It should race then settle down to approx. 600 RPM. That's assuming the ISC is working as it should and the TPS is set correctly. I dont believe the 84 has an idle relearn procedure. GET A FACTORY SERVICE MANUAL!!
 

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1985 eldorado biarritz convertible
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151 Posts
To set idle speed. Remove air filter and lay over to the side, vacuum hose left connected to it. Now locate the idle speed motor.( ISC) With the engine running, lift the throttle lever to clear the idle motor shaft. Once clear, press firmly on the shaft with your other hand, keeping constant pressure on it till it fully retracts. Once retracted, QUICKLY remove the electrical connector to it. Now let the throttle lever come back to rest. It should idle at about 400 RPM. Shut off the engine. Measure the clearance between the throttle lever and idle motor shaft. It should be 60 thousands measured with a feeler gauge. If no clearance, rotate the shaft in with a pair of pliers to get that clearance. Now, reconnect the electrical connector. Restart the engine. It should race then settle down to approx. 600 RPM. That's assuming the ISC is working as it should and the TPS is set correctly. I dont believe the 84 has an idle relearn procedure. GET A FACTORY SERVICE MANUAL!!
yes, this is the procedure i reffered to as "re-learn". i can attest the procedure worked as intended.
 

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1984 Eldorado
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42 Posts
Discussion Starter #7
Thanks Carnut. I have a factory service manual, but it's still in storage. I will be able to retrieve it in about four more months once my house is finished. I'll follow your instructions and see what happens. I just hope no parts are defective. Germany is a long way from the States!!!
 

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1985 Cadillac Seville
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5 Posts
Here is some additional info on high idle/pulsating idle/fluctuation idle on the HT 4100. I have an 85 Seville that ran nicely when I got it, but not perfectly. After several months of replacing parts and making adjustments, I finally got it running like a new car.

In addition to some of the comments here, to get the car running right I had to:
-Replace the Coolant Temperature sensor and pigtail
-Replace the MAT sensor and pigtail
-The wires in the distributor were cracked/loose. I replaced the entire distributor to be safe, new Accel coil, new hi-perf plug wires, and of course new ignition module
-Replaced all Vacuum lines, and made sure the lines went to the right places (used the manf manual)
-Replaced the ISC Motor and adjusted per the manual
-SET THE TIMING. This was my biggest issue with the idle pulsating. Turns our when I got the car the timing was retarded about 6 degrees. Replacing the dist and setting the timing correctly made it go from running like a 30 year old car to a new car.
- I also replace the injectors, fuel filter, cat converter, and exhaust. Everything works together.
-There's a "minimum idle" adjustment screw that's built into the throttle body housing. You have to have the hands of a 5 year old and be a contortionist, but you can adjust that down to the correct low idle, then reset the ISC per the manual. It uses a Torx head screw, of course, to make it even more fun.

Hope this helps someone down the road.
-CP
 
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