Barry94

Idle Speed Control (ISC)

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I haven't posted anything technical for some time now.

Dare I mention how well the STS has been working for the past few years.

During the past few days my idle had become very erratic. The idle was ranging from 700 - 3000 rpm.

The engine would speed up and down while in park and also while driving and slowing to down,

just about the time you wanted to stop, it would rev and you needed to be quick on the brake.

I suspected the ISC was the problem.

I entered the Onboard Diagnostics and set it to monitor the Throttle Position Switch (P172)

Sure enough, without the throttle depressed, the switch was intermittently switching from Lo to Hi.

(With no pressure on the throttle it should remain Lo)

Description of ISC.

When the throttle is released it depresses the plunger on the ISC, this closes a switch in the

ISC to signal the computer that the throttle has been released and to go to the idle mode.

If the switch is not closed when the throttle is released, then the engine "hunts" and doesn't

know what to do, hence the ranging of rpms.

I removed the ISC module.

Three 8mm nuts (stainless), don't loose the lock washers.

Note: Remove the two nuts on the shift cable bracket and move the cable to the side

to gain better access to the bottom nut on the ISC.

On the ISC module remove the three studs holding it together.

Once separated, you will see a set of points off to the side. This is the switch.

I used a small folded piece of 2000 grit sandpaper and placed it between the points,

then manually closed the points and gave them a rub with the sand paper.

Then, after, gave them a shot of contact cleaner.

I cleaned and greased all the gears, then reassembled the unit.

I installed the ISC and it worked fine.

I suspect dirt or some foreign material had gotten on the point contact surface

causing intermittent contact.

The point gap and actuation seemed fine.

Not sure how to attach multiple pictures to a single post.

If only one shows, see following posts.

Barry

post-6-1129781522_thumb.jpg

Edited by Barry94

2008 STS V8
2016 Colorado Z71
1970 Corvette LT-1 Coupe

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I used a small folded piece of 2000 grit sandpaper and placed it between the points, then manually closed the points and gave them a rub with the sand paper . . . . Then, after, gave them a shot of contact cleaner . . . . I installed the ISC and it worked fine . . . . I suspect dirt or some foreign material had gotten on the point contact surface causing intermittent contact.

Congratulations on using such a fine grit paper. THAT was important. And I suspect you know it.

Many folk think they can just file or sand ANY contacts to bring them back to life. And, of course, they do revive . . . . for a week or two.

What people often don't realize is that by filing contacts they have enormously increased the surface-to-air ratio of the contacts. Perhaps hundreds fold or more. This promotes rapid oxidation, i.e. rust. That's shortly followed by even worse contact resistance.

The best solution is to use a "burnishing" tool or apply that contact cleaner to a strip of paper or very thin leather and draw it repeatedly back and forth between the closed contacts.

You'll wind up with clean contacts without developing the extra surface area that promotes rust and even worse problems than you started with.

Regards,

Warren


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There is no means of avoiding the final collapse of a boom brought about by credit expansion. The alternative is only whether the crisis should come sooner as the result of a voluntary abandonment of further credit expansion, or later as a final and total catastrophe of the currency system involved. - Ludwig von Mises

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A very helpful post.

Thanks Barry94!

Regards,

Warren


Posted Image

There is no means of avoiding the final collapse of a boom brought about by credit expansion. The alternative is only whether the crisis should come sooner as the result of a voluntary abandonment of further credit expansion, or later as a final and total catastrophe of the currency system involved. - Ludwig von Mises

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I used a small folded piece of 2000 grit sandpaper and placed it between the points, then manually closed the points and gave them a rub with the sand paper  . . . .  Then, after, gave them a shot of contact cleaner  . . . .  I installed the ISC and it worked fine  . . . .  I suspect dirt or some foreign material had gotten on the point contact surface causing intermittent contact.

Congratulations on using such a fine grit paper. THAT was important. And I suspect you know it.

Many folk think they can just file or sand ANY contacts to bring them back to life. And, of course, they do revive . . . . for a week or two.

What people often don't realize is that by filing contacts they have enormously increased the surface-to-air ratio of the contacts. Perhaps hundreds fold or more. This promotes rapid oxidation, i.e. rust. That's shortly followed by even worse contact resistance.

The best solution is to use a "burnishing" tool or apply that contact cleaner to a strip of paper or very thin leather and draw it repeatedly back and forth between the closed contacts.

You'll wind up with clean contacts without developing the extra surface area that promotes rust and even worse problems than you started with.

Regards,

Warren

Good point on the contact cleaner and a piece of paper. When cleaning points on a point type ignition on a snowmobile, it would do the same thing if you filed the points. Piece of paper and some contact or brake cleaner does the trick.

Spence

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Thank you Barry.

I thought that trottle switch placed somewhere under the trottle pedal.

Now I know.

Good job.

We need more posts like this one. biggrin.gif

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I used a small folded piece of 2000 grit sandpaper and placed it between the points, then manually closed the points and gave them a rub with the sand paper  . . . .  Then, after, gave them a shot of contact cleaner  . . . .  I installed the ISC and it worked fine  . . . .   I suspect dirt or some foreign material had gotten on the point contact surface causing intermittent contact.

Congratulations on using such a fine grit paper. THAT was important. And I suspect you know it.

Many folk think they can just file or sand ANY contacts to bring them back to life. And, of course, they do revive . . . . for a week or two.

What people often don't realize is that by filing contacts they have enormously increased the surface-to-air ratio of the contacts. Perhaps hundreds fold or more. This promotes rapid oxidation, i.e. rust. That's shortly followed by even worse contact resistance.

The best solution is to use a "burnishing" tool or apply that contact cleaner to a strip of paper or very thin leather and draw it repeatedly back and forth between the closed contacts.

You'll wind up with clean contacts without developing the extra surface area that promotes rust and even worse problems than you started with.

Regards,

Warren

Good point on the contact cleaner and a piece of paper. When cleaning points on a point type ignition on a snowmobile, it would do the same thing if you filed the points. Piece of paper and some contact or brake cleaner does the trick.

Spence

Spence,

Out of curiousity, how old of snowmobile do you have that has ignition points???


Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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You are right Brry, the stuff insid ethe ISC motor does not wear out badly but rather needs service - cleaning, greasing etc. Good job.


The saddest thing in life is wasted talent

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Thanks Kger2 for managing the pictures, and also thanks Bruce for doing that as well.

This site has given me such great information.

Normally when I have a problem, I just go ahead and fix it.

This time I remembered the camera.

Posting this repair is the least I can do to help others on this site.

Barry


2008 STS V8
2016 Colorado Z71
1970 Corvette LT-1 Coupe

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Glad I could help out Barry......but I fail to see what I did laugh.gifwink.gif . Big Brotha (Bruce) really tidied and snazzed up your work. It's all your work and effort that shows at the end. You have a great looking and very informative thread. Thanks for taking the time Barry. smile.gif


"Burns" rubber

" I've never considered myself to be all that conservative, but it seems the more liberal some people get the more conservative I become. "

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thanks to each of you who have responded to my post "surgeing", . the caddy goes back to the mechanic today , I will be armed with all this info that each of you have shared . I thank all of you for your contributions. I will keep you posted. once the problem is solved I can smile again. thirty days without my eldo is like being tied down for a month. wink.gif hi ho hi ho its off to the shop we go. myeldog

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Good luck let us know how it works out...


Early on sailors navigated by the stars at night and the North star became the symbol for finding ones way home. Once you know where the Northstar is you can point your ship in the right direction to get home. So the star became a symbol for finding ones way home or more symbolically even finding ones path in life.

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Yesterday, I took apart the ISC motor and gave it a cleaning, lube, and light sanding of the contact point with 320 grit wet-dry sand paper. Now, I no longer have surging and idling problems. Thank you Barry94 for the heads up about servicing the ISC motor. I was also having problems with the tachometer jumping and a loss of power causing the car to stall at idle. It looks like that problem is also solved. One thing I did do was break the clip which secures the ISC harness, since the plastic was brittle from all the engine heat over the years. I'll either try to epoxy it together or buy a new harness connection.

Edited by MAC

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Yesterday, I took apart the ISC motor and gave it a cleaning, lube, and light sanding of the contact point with 320 grit wet-dry sand paper. Now, I no longer have surging and idling problems. Thank you Barry94 for the heads up about servicing the ISC motor. I was also having problems with the tachometer jumping and a loss of power causing the car to stall at idle. It looks like that problem is also solved. One thing I did do was break the clip which secures the ISC harness, since the plastic was brittle from all the engine heat over the years. I'll either try to epoxy it together or buy a new harness connection.

Good to hear that solved your problem. I had hoped that posting that information might help someone someday.

Barry


2008 STS V8
2016 Colorado Z71
1970 Corvette LT-1 Coupe

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Thank you for this post. I have had the problem intermeittantly for years. The dealer just gave me a quote of $3,400 to replace all the things they think it 'could' be. They charged $72 for a road test and could not duplicate it. I love this baby and will do some more research on how to find this and pull it and clean it. Thanks

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Thank you for this post. I have had the problem intermeittantly for years. The dealer just gave me a quote of $3,400 to replace all the things they think it 'could' be. They charged $72 for a road test and could not duplicate it. I love this baby and will do some more research on how to find this and pull it and clean it. Thanks

Just to let you know, I eventually had to replace the ISC motor even after I cleaned the contacts. Once I installed the new one the erratic idling stopped. The cleaning did help initially but it wasn't a long-term fix. Success by cleaning the contacts may vary, so it may be worth a try.

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I just took one apart, there are 2 long bolts.  Here is my thread

 


Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Thanks Cadillac Mike ! That is exactly what I needed. Also Thanks for the follow up on that reference thread. Being that the cleaning of the ISC motor may be only a temporary fix and new ones may need to swap over an adjustable screw after careful measurement.

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Anytime, let us know how it turns out.

Other makes of the ISC may include the adjustment screw I used a Standard product, it wasn't the cheapest "value" unit, it was a step up and worked fine.  He was selling the car, so he wanted to keep the cost down.


Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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