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Discussion Starter · #1 ·
Greetings,

I have a 85 El Dorado that was my moms car. I bought it from her estate after it had been sitting in her pole barn for about 20 years. It wouldn't start so I put new (rebuilt) TBI's in it and fuel filter, tank and fuel pump. That got it running.

It is a real solid car with original paint and just over 100K miles. After only driving it up and down the street a few times I finally decided it was ready for a slightly longer road trip so I took my wife out to dinner in it about 10 miles away. It ran fine on the way out but on the way back I went to stop for a traffic signal and it felt like I had my foot on the gas pedal yet. When I finally jammed on the brakes it stalled out the engine. When the light turned green I started it and put it in drive as fast as I could and made it home.

It still wants to idle way way too fast. Does anyone have any words of wisdom as to what could be causing this? I googled it and came up with some hits about the idle control motor but it seems odd that it would run that fast.

Hopefully I can figure this out so I can move the car out of my regular garage as I don't even want to start it until I get this sorted out.

Thanks everyone.
 

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2001 Deville
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Yep, also .check the throttle cable, cruise linkage.If you don't find anything remove the IAC, manually extend the pintle and reinstall and see if that fixes it. it may just be "stuck" but if it happens again replace it. When checking the cable/linkage remove the air cleaner and look at the throttle plates, they should be completely closed. It is a remote possibility that 1 of the throttle plates has come loose
 

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Discussion Starter · #6 ·
Dogbisquit, I'll check those things all out when I get home tomorrow. I'm not real sure what the pintle is that you spoke of though.

Smoke, Actually my brother replaced the tank, pump and TBI's so I don't know if he followed any procedures but his brother in law is an ex Cadillac dealership mechanic and was his guide on it. I ran it at home for a short time and then stored it for the winter. When I tried to run it in the spring it wouldn't run. I found a burnt out fuel pump fuse. Turns out that the stud for the fuel gauge was a little long and was shorting out on the body so I turned a small nylon button to put over it. I also replaced the fuel filter and it ran like a champ on the way to dinner but on the way back it started to run way too fast.

Thanks guys for the quick responses and I'll post anything that I find out about it.
 

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2001 Deville
2004 Deville
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On the end of the Idle air control if it has 1 there is a pintle, its a knob looking thing that retracts and extends basicly controlling a vacuum leak to control the idle speed. I forgot that you have an old school set up with an ISC motor which also could be getting stuck
 

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1984 Eldorado Biarritz, 1983 Sedan deVille
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These were before the IAC. They just have the clunky ISC. I don’t think the HT ever got idle air control. Maybe on the port injection, but not sure. Too bad because it works a lot better.
 

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Discussion Starter · #10 ·
I finally made it back to take a look at the 4100 and it appears that the ISC motor is stuck or something along those lines. I looked down at the butterflies and they look to be open about 1/16 inch when it is in idle position. It doesn't appear to move when I turn the key on. I did unplug it and plug it back in just in case there was a little corrosion but it looked good.

I'm wondering if there is any way of checking it without just putting a new one on and hoping it works.

I did also turn the screw that is in the ISC to slow it down a little bit and I've wondered if I can just screw it in until it idles at the proper speed but that still doesn't explain why it was idling at a normal speed and all of the sudden idle at 2K rpm faster.
 

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1984 Eldorado Biarritz, 1983 Sedan deVille
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Either a failed throttle closed switch (probably) or extremely gummed up gears in the ISC (unlikely). With your foot off the gas, car in diagnostics, is the Lo light on on the climate control? Does it go out when you push the throttle?

It needs the ISC to idle right, don’t just crank on the screw.
 

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1985 Eldorado ASC convertible, HT4100
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Re: "Being that you changed the throttle body, did you follow all the steps to set the TPS, minimum air, and ISC?"

Hi Big B, this is a necessary and somewhat complex process. Can't just replace the parts, need to calibrate them. (Shop miscalibrated mine and it didn't get enough gas and stalled, instead of too much... ) The steps are spelled out in the Factory Service Manual, which you should have if you're gonna do work on it. Cheapest on eBay currently this one, $25 shipped:
Factory OEM 1985 Cadillac Brougham Eldorado Seville Final Edition Service Manual | eBay
 

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Discussion Starter · #13 ·
Smokus, Is the throttle closed switch part of the ISC? I don't see any other switches there. I turned the key on and under Auto the low light is on but when I hit the gas it stays on. I'm not sure what you mean about diagnostic mode. I kind of figured the screw would need to be put back where it was but wanted to be sure that turning it in a little would slow the engine down.

Scott. It was actually my brother that installed the new TBI units and his brother in law is a retired Cadillac mechanic and likely helped him through the setup of them. It ran fine the half dozen or so times that I took it up and down the street but when I went for a ten mile drive to go for dinner it started running fast on the way home. I could be wrong but it seems like if it needed calibration it would be off to begin with.

I really appreciate you guys helping me try to get this Eldo going again. It sure doesn't seem to do a car much good to park it for 20 years even if it is in a clean dry place.
 

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1981 Biarritz V864, 1981 Seville V864
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This is from a Cadillac pocket troubleshooting guide. Once you get into the diagnostics mode you can activate the ISC motor to extend and retract repeatedly by following the steps shown to see if it is operating smoothly. The factory Service Manual would detail how it works more clearly and is well worth the money but this should give you an idea of what Smokus is talking about. Dave

Font Rectangle Pattern Paper Paper product
Rectangle Font Parallel Pattern Schematic
 

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1984 Eldorado Biarritz, 1983 Sedan deVille
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Smokus, Is the throttle closed switch part of the ISC? I don't see any other switches there. I turned the key on and under Auto the low light is on but when I hit the gas it stays on. I'm not sure what you mean about diagnostic mode. I kind of figured the screw would need to be put back where it was but wanted to be sure that turning it in a little would slow the engine down.

Scott. It was actually my brother that installed the new TBI units and his brother in law is a retired Cadillac mechanic and likely helped him through the setup of them. It ran fine the half dozen or so times that I took it up and down the street but when I went for a ten mile drive to go for dinner it started running fast on the way home. I could be wrong but it seems like if it needed calibration it would be off to begin with.

I really appreciate you guys helping me try to get this Eldo going again. It sure doesn't seem to do a car much good to park it for 20 years even if it is in a clean dry place.
Yes, the throttle switch is part of the ISC. move the throttle arm out of the way and press on the plunger-you should feel a clink when you push on it. As mentioned, it’s in your interest to have a factory manual. Diagnostics can be accessed by holding OFF and WARMER on the climate control head.
 

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Discussion Starter · #17 ·
I did the diagnostic and it showed a code of 27 and 52. Not exactly sure what those codes mean but I did see that on some GM cars a 52 just means that the battery has been disconnected. I also just ordered a factory service manual for it so hopefully that will give me some info too.
 

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Discussion Starter · #18 ·
Yes, the throttle switch is part of the ISC. move the throttle arm out of the way and press on the plunger-you should feel a clink when you push on it. As mentioned, it’s in your interest to have a factory manual. Diagnostics can be accessed by holding OFF and WARMER on the climate control head.
I did the diagnostics and it showed codes of 27 and 52. I also ordered a factory service manual so hopefully that will show me how to trigger the ISC and see if it's good or not. I hate just buying parts without knowing if they need replacing or not.
 

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1981 Biarritz V864, 1981 Seville V864
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This is a video of someone that used to post on this Forum testing his ISC motor in diagnostics mode. Please read his comment below the video to get more detail but in this mode it also tests a number of other ECM controlled functions.


The diagnostic mode can also display a number of sensor input values that the ECM is seeing while the car is running so if you can repeat the high idle situation you could monitor the appropriate one(s) to see if it is giving a bad reading and telling the ECM to increase the idle speed. Another thing that will increase the idle speed is if the ECM sees that the A/C compressor has turned on.

The attached scan is from a training manual for the 1981 Digital Fuel Injection system which would be the same as the system used on your 85. Hopefully it will give you some insight into what could affect the idle speed. Interestingly it indicates that idle speed will also be increased if the car starts running at high temperature. Maybe on your return trip the engine got hot enough to put it into this mode? Dave
 

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