Barry94 Posted October 20, 2005 Report Share Posted October 20, 2005 (edited) 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 Edited October 20, 2005 by Barry94 Quote 2008 STS V82016 Colorado Z711970 Corvette LT-1 Coupe Link to comment Share on other sites More sharing options...
Barry94 Posted October 20, 2005 Author Report Share Posted October 20, 2005 ISC Apart Quote 2008 STS V82016 Colorado Z711970 Corvette LT-1 Coupe Link to comment Share on other sites More sharing options...
Barry94 Posted October 20, 2005 Author Report Share Posted October 20, 2005 Location of Points Quote 2008 STS V82016 Colorado Z711970 Corvette LT-1 Coupe Link to comment Share on other sites More sharing options...
Barry94 Posted October 20, 2005 Author Report Share Posted October 20, 2005 ISC Apart Quote 2008 STS V82016 Colorado Z711970 Corvette LT-1 Coupe Link to comment Share on other sites More sharing options...
Barry94 Posted October 20, 2005 Author Report Share Posted October 20, 2005 ISC Out Quote 2008 STS V82016 Colorado Z711970 Corvette LT-1 Coupe Link to comment Share on other sites More sharing options...
WarrenJ Posted October 20, 2005 Report Share Posted October 20, 2005 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 Quote 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 Link to comment Share on other sites More sharing options...
WarrenJ Posted October 20, 2005 Report Share Posted October 20, 2005 A very helpful post. Thanks Barry94! Regards, Warren Quote 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 Link to comment Share on other sites More sharing options...
Ed Fenwick Posted October 20, 2005 Report Share Posted October 20, 2005 Good post Barry, these are good cars and a little cleaning and adjustment works wonders doesn't it? Ed Quote Link to comment Share on other sites More sharing options...
67coupedeville Posted October 20, 2005 Report Share Posted October 20, 2005 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 Quote Link to comment Share on other sites More sharing options...
Oldgamer Posted October 20, 2005 Report Share Posted October 20, 2005 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. Quote Link to comment Share on other sites More sharing options...
KHE Posted October 21, 2005 Report Share Posted October 21, 2005 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??? Quote Kevin '93 Fleetwood Brougham '05 Deville '04 Deville 2013 Silverado Z71 Link to comment Share on other sites More sharing options...
adallak Posted October 21, 2005 Report Share Posted October 21, 2005 You are right Brry, the stuff insid ethe ISC motor does not wear out badly but rather needs service - cleaning, greasing etc. Good job. Quote The saddest thing in life is wasted talent Link to comment Share on other sites More sharing options...
Barry94 Posted October 21, 2005 Author Report Share Posted October 21, 2005 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 Quote 2008 STS V82016 Colorado Z711970 Corvette LT-1 Coupe Link to comment Share on other sites More sharing options...
Regis Posted October 21, 2005 Report Share Posted October 21, 2005 Glad I could help out Barry......but I fail to see what I did . 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. Quote "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. " Link to comment Share on other sites More sharing options...
myeldog Posted October 26, 2005 Report Share Posted October 26, 2005 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. hi ho hi ho its off to the shop we go. myeldog Quote Link to comment Share on other sites More sharing options...
Scotty Posted October 26, 2005 Report Share Posted October 26, 2005 Good luck let us know how it works out... Quote Link to comment Share on other sites More sharing options...
MAC Posted July 17, 2006 Report Share Posted July 17, 2006 (edited) 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 July 17, 2006 by MAC Quote Link to comment Share on other sites More sharing options...
Barry94 Posted July 20, 2006 Author Report Share Posted July 20, 2006 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 Quote 2008 STS V82016 Colorado Z711970 Corvette LT-1 Coupe Link to comment Share on other sites More sharing options...
tekapo Posted April 2, 2009 Report Share Posted April 2, 2009 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 Quote Link to comment Share on other sites More sharing options...
MAC Posted April 2, 2009 Report Share Posted April 2, 2009 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. Quote Link to comment Share on other sites More sharing options...
the gold2 Posted December 2, 2016 Report Share Posted December 2, 2016 Great thread but how does one open up the ISC motor? Does the casing drop back from the face plate and bolt or does the bolt require removal first? Quote Link to comment Share on other sites More sharing options...
BodybyFisher Posted December 2, 2016 Report Share Posted December 2, 2016 I just took one apart, there are 2 long bolts. Here is my thread Quote 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 Link to comment Share on other sites More sharing options...
the gold2 Posted December 2, 2016 Report Share Posted December 2, 2016 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. Quote Link to comment Share on other sites More sharing options...
BodybyFisher Posted December 2, 2016 Report Share Posted December 2, 2016 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. Quote 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 Link to comment Share on other sites More sharing options...
the gold2 Posted December 10, 2016 Report Share Posted December 10, 2016 Just updated on the other thread, added an extra image bc I was not allowed to load three images in the referred thread. Quote Link to comment Share on other sites More sharing options...
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