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Problem: Fast idle, about 1,200 RPM in drive and 3,000 RPM in Neutral.   Intermittently at first, first time was a surprise. 

Historically I know that on the pre-1996 Northstars, this is due to the ISC Motor or Idle Speed Control.   Our friend and member @Barry94  did a terrific write-up back in 2005 that has always been helpful in understanding and diagnosing the ISC motor.  This thread was a walk down memory lane for me.  So many members I had gotten to know in this thread, that contributed so much to making caddyinfo the terrific resource it is, their help and knowledge is preserved in threads like this, I miss them all. My name in this thread is Scotty (retired).   Barry's outstanding writeup is here:

Removal of the ISC motor was a lot harder than I recall from 91 Seville.   There are three nuts to remove it once the cruise control servo is removed, one of which is difficult to get at.   If I had a throttle body to intake o-ring, I would have removed the throttle body to make it easier.   Important TIP, never remove the throttle body without having a replacement o-ring on hand.  Once you remove the throttle body, the rubber O-ring expands SOO much that it is unusable and cannot be reinstalled.   The heat, fuel and oil must swell the rubber and as long as its contained, all is good, haha, but remove it and its like a Jack in the Box or Can of Snakes, bam, now too big to go back...  don't ask me how I know that  :fighting0025:

 Here are the parts disassembled, it was terribly dirty, the grease was dried out and the unit was very worn out. No doubt this is either the original, or it has done its job well for a very long time. 

DSCN9902_zpssaasamz5.jpg

Other than being very worn, I didn't see anything that would have caused my high idle, the closed throttle contacts looked good and tested good with an ohm meter.  But the commutator was worn very bad, it had sort of a valley worn into it from the brushes as seen here (bad photo, I know, sorry).  This is an interesting motor in that the commutator is oriented as a disk or turntable that the brushes skate on verses the typical motors we are used to where the commutator is a rotating cylinder with the brushes from the sides.

DSCN9906_zpslfejacen.jpg

Badly worn washer/ring, grooved

DSCN9910_zpsgsk5y6df.jpg

Stator and magnets.   The 'bearing' at the bottom was dry and sticky.

DSCN9909_zpsavctgvjw.jpg

Two brush holes, note spring stuck in hole, I had hoped that this was my problem that the spring was not supplying adequate pressure given the commutator wear. In actuality, that might by the problem here, the commutator turntable was worn so badly that there was a groove, that groove causes the brush to apply less pressure as the spring is less compressed and the brush sticks out further causing less stability in the brush.   I don't think this ISC is salvageable.

DSCN9905_zpsjm9yjtvh.jpg

Gears gummed up

DSCN9907_zpsmm0jbi2u.jpg

I didn't have a whole lot of hope that I could fix this unit given the wear and that I didn't find a problem besides the bad wear.  This unit owes the owner nothing.  But I cleaned it up really good, lubed it up and reassembled it. Getting that lower nut on is NO fun, good thing I have the dexterity of a brain surgeon :ninja: but make sure you cover the area below the nut, if you drop the nut, kiss it goodbye, it ends up down by the steering rack lost forever :lol: (don't ask me how I know that its an M5 nut :blink:) << hands of a surgeon?

  No good..  engine still racing today intermittantly.  Ordered new one from Rockauto, arrives tomorrow.   To be continued.    Its time for a new camera

 

 

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  • 1 month later...

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To complete this thread, I ordered a Standard Motor parts ISC from rockauto, installed it and the idle is perfect, no more fast idle, and coming to a stop and stop lights are uneventful.

The new ISC did not come with the adjustable plunger.  I used the plunger from the prior, making sure that the plunger was in the EXACT location by counting threads and measuring it with a gauge.   With the throttle body cleaning, the engine is no smooth and responsive.

Pre-1995 - DTC codes OBD1  >>

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

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  • 2 months later...

Well I took apart the ISC motor from the junkyard.

It was quite easy but I did not force the motor housing off because I was not sure what to expect with springs and brushes flying apart.

 

I am not sure what to make of this posssible 'spare' motor.

 

Obviously the gears have dried grease. There is a spring loaded circular clip that has some dry grease on it but also some other surface material that I am not sure whether its metallic or just more dry grease. (This lies around the bolt that moves to adjust the idle.)

Nor do I know how to interpret what I see.

i.e. perishing unit or possible good spare after cleaning dry grease and regreasing..

The contact points seem to look ok. No burnt marks. But no black carbon surface points. Just metal.

 

Is there a way to connect a 9 volt battery onto the harness of this spare in order to make the motor work?

 

Pictures attached. Thanks Cadillac Mike !

 

DSCN5622.jpg

DSCN5623.jpg

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Other than the dried up grease it looks pretty good and the gears look good and you are correct the closed throttle contacts look good, overall much better than mine above.  The motor housing should pry right off. look at mine above, nothing will fly around, there are springs behind the brushes but you can just replace them if they fall out.   This way you can clean up the commutator up and check the brushes.    How much did you pay?

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

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OK, I will clean it up.

At the pick n pull salvage yard  it was like $15 with harness. Its off a 4.9 liter Caddy engine.

 

In my mind, it was simply a shot at having a spare and an academic exercise in removing it from a car and also looking inside the mechanism.

 

You are correct that the torx screws are tricky to reach ! I also kept the Torx screws for this 'spare'.

 

OK just read the other post regarding grease type. Thanks !!

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  • 4 months later...

Cadillac Mike, I am finally addressing my idle problem. I have been busy.

I plan on testing the current ISC (58K original miles) but I also have a used replacment on hand that has been cleaned and lubed with Lubriplate.

 

My question at this point is, after removal and cleaning of the current ISC, do I have to run a calibration routine after re-installation-(not having touched or altered the plunger length) ?  Or is it a drop in task with subsequent Idle relearn routine?

 

Thanks

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Sorry, I did not see this.  If you didnt touch the plunger length you should be fine.  

Let us know how this works out

The best thing to do to get a members attention is to direct it to them, like this @BodybyFisher.  Ill get a notificaion on my email.  Thx

@the gold2 

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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Hello BodybyFisher, thank you for the follow up. I released the ISC bracket from the throttle body (two T25 screws-but kind of tight small area) but decided to just open the ISC up on the car and clean and lube. The harness end to the ISC had a brittle hasp and broke. Fortunately the internal rubber gasket was good and tight. I reinforced the plastic harness body at that end with glue.

The other end of the harness was not coming undone easily so I did not want to pursue this in order to avoid a broken harness body. (plug).

 

I can easily do the work while the harness is still attached to the ISC. I put a rag under the T25 screws to catch any strays. Likewise I will use a magnetic tray and set up an 'operation field' for the work to be clean. Will continue later. Been busy lately.

 

I will not turn the plunger so it will remain intact. Hopefully it will drop back in with no resetting routine.

 

My car has a periodic high idle followed by the Check engine Light. E030 is the code. meaning that the ISC is suspect. The other day the car operated just fine. Real smooth in fact. It was nice driving it after so long. Several parking stops that day. No problems. Next day it lingered on a 1100 to 1200 idle again at start up before dropping down. It elicited the CEL.  On other days in the past, the idle would be about that high and linger longer with 'sailing'.

 

So I hope to resolve it by cleaning and fresh  lubriplate.

 

I will follow up with results.  http://caddyinfo.ipbhost.com/index.php?/profile/2998-bodybyfisher/

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I think I noted that I bought the cheaper Standard Motors product and she worked fine.  If it gives you ary difficulty replacing it makes a big difference.  

If you go that route measure and count the turns of the plunger.  If I recall it used the old plunger.

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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OK Bodybyfisher, I checked out the exisiting ISC (56K miles-original) and it looked good inside. The contact points of the switch were nice and clean. The grease was a bit fudgey but not hard. I cleaned it carefully and relubed with Lubriplate. Also a bit of lube onto the gears, which were in excellent shape.

I used blue tape over the plunger and boot before ISC disassembly in order to make sure it was not moved at all. Also black marker on the head face with an orientation arrow. Put the two halves together and bolted up. Nothing bound up while putting the halves together. So I doubt a gear got jammed.  The plunger retained its 'to and fro spring action'.

 

So after carefully attaching it to the throttle body and buttoning up everything, the start up elicited a 1500 RPM idle. (it used to start up at around 1100 and drop some after the CEL went on).

It still activates the E030 code. I did some peripheral diagnostic checks as per factory book.  First off the cables are not binding etc.

The E030 diag tree states that if E055 is in history (only elicited once some months ago after several E033)  then I need to go to E055 chart. That chart says not to use that same chart test if code E030 are current or history but to use procedures for codes E021,E026 or E030... So the E021 test passes, so does the E026 test.

 

Arbitrarily Following the ISC Max Extension Adjustment protocol (6E-C2-16) I got the value of 2.5 for the ED01 'TPS'. (later I got 2.9  Note: a few days ago, before removing the ISC I was able to get a value of 'negative 0.6' ED01 ,when simply scrolling through the ECM Data)

So it recommends turning the ISC plunger counter clockwise until the acceptable TPS parameter of 13.4  is had.

 

At this point I have not done the full E030 diagnostic  routine primarily because it seems like I need another person at the engine bay to observe the ISC.

Also the book directives are a bit confusing.

 

If I should dare to turn the ISC plunger, I would like to ask how to do this. I did try a bit with a needle nose plier but it did not budge and I did not want to force anything.

Is that threaded plunger turntable while the ISC is installed?

 

So at this point I am hoping that the plunger can be adjusted and that this will satisfy the E033 situation.

I know that it would be wise to ascertain that the ISC is moving but it seems like I need a second person to observe while I hit the test button on the on board diagnostics.

 

Another issue is that on one part of a diagnostic tree it requires disconnecting the ISC harness.

 

OH BOY ! With that harness plastic kind of brittle I wonder how to disconnect it from the far end aspect without messing up. Do I use a sharp pick to pull out and away?

My background with the mechanics of this car is minimal. I do what I can, so I have no historical background and savvy to fall back on.

 

Bodybyfisher, can you advise on this?

 

(even if I buy a new ISC, I somehow feel that it won't be the solution.)

 

Thanks !

 

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I see you are here, Ill come back later.   The landscapers just kicked up a rock and broke a window on my wifes Audi Q5, I have to put something over it in case it rains.....always something.....part $275, installation by Audi.....who knows

Ill talk later

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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OK, I searched for the Guru's adjustment method, @adallak had posted it a while back, try adjusting your ISC like this, and see how this works for you.

 

Here is the ISC motor adjustment procedure for 4.9 liter engine outlined by the Guru. It should be the same for 94 Northstar. The gap is probably 0.060".

"Hold the throttle lever open manually to get the RPM to about 2500 or so. Simultaneously depress the plunger on the idle speed control motor so that it starts retracting. Keep forcing the plunger to retract until it fully retracts and stops. Disconnect the wire connector to the idle speed control motor to "freeze" it.

Return the throttle to the closed bore idle position. Use that torx screw that you have been jacking on to lower the idle to 450-500 RPM. 450 is the desired setting. The idle should come down to 450 and there should still be clearance to the ISC motor plunger. Nothing (like cruise control or throttle cable) should keep the throttle lever from going down to the 450 idle point.

Idling at 450 with the ISC motor fully retracted turn the plunger until there is a .030 gap between the plunger and the throttle lever.

Check the cruise link while at the 450 idle point. It should just be barely snug with a tiny bit of slack in the link. Make sure that there is a little slack when you adjust it. There MUST be some....just a little but some slack.

Plug in the idle speed control motor connector and cycle the key off.

Disconnect the battery negative cable for 60 seconds to erase any idle learn offsets that have been stored. Cycle the key on for 30 seconds and then off. Wait 60 seconds. Cycle the key again."

If there is still no gap, unscrew the plunger and cut it or try the plunger from the old motor. That's what I had to do with one of three ISC motors I installed on my 4.9 in ten years.

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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Bodybyfisher, thank you very much for taking the time out between broken windshields, wayward gardeners and idle challenged Eldorados !

I tried to see if disconnecting the battery for a day would make a change but it made no difference. No luck with Idle reset etc.

I wiggled the wire harness around but no observable difference.

 

So thanks to adallak, I will fashion the home made special tool and attempt to adjust the ISC plunger.

 

If that does not work, then it is off to go through the routine you advised for above.

 

QUESTION, although I doubt it, would a trickle charger be able to damage the PCM main computer? (car off always with trickle charger- good quality one.) Just another avenue to consider because I have a spare computer...

 

Thank You !

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I doubt very much that it could damage the PCM.

Is the ISC not retracting?

Does it ratchet or click?

When the linkage hits the plunger, it closes the contacts and retracts the plunger, does that happen?  Try that test above, 2000 rpm, depress plunger manually and plunger should retract.

Be sure throttle body throat and plate are clean and gook is not holding the plate open.  Be sure that the plate fully closes.

@the gold2

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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Thank you for the follow up. I will try these tests as soon as I can get my friend to add a second pair of eyes and hands.

Thus far I hear no ratcheting and the inside of this original ISC unit (58K miles) was clean and the gears and contacts were very sound.

The spare ISC I have has more time of use but the gears are sound and likewise the contacts are clean.

 

More fiddling with this baby later. I need to make sure it is retracting and also wiggle the wire harness while testing it. I would then need to rule out the harness with a multi meter, I suppose...

 

I will update after a while.

Glad to hear that the computer is most likely not a probable problem source.

 

Thanks again !

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When you took it apart, you noticed that the commutator is not a typical cylinder with the brushes riding on the sides, but a flat one like an LP record where the brushes faced down, how did the face of the.commutator look?

@the gold2

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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Hi BodybyFisher, that is one thing I did not look at with the onboard (less used) one. If I observe that the plunger is not working, I plan to remove the onboard  ISC again and open her up again to recheck and this time look at the commutator.

Thank you, your help is extremely appreciated !

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It's only two screws, if the commutator is dished, I found that it didnt work well, I think the brushes don't make as good a contact.  

Do your test to see if it retracts and let me know how it goes.

If you have never cleaned the throttle body, a dirty TB in my 96 with an IAC caused my idle to be around 1200 in gear.  A good clean of the TB cleared that up.

@the gold2

 

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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Will do ! Actually I had been keen on keeping the throttle body and blades clean. I must have cleaned 3 times in the past two - four months (undo battery afterward and do relearn routine) just to make sure about that variable as I tinkered. Generally the engine is very very clean.

 

Right now I have another car to do some brake job on and other routine maintenance.... So the caddy sits as a primadonna until I have time to resume.

 

Thank You !!

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At least take the snorkle off and look at the plate, don't just clean what you.can see, clean the.back of the plate and the edges. 

With the plate off you will be able to see clearly if it is hanging open

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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Hi, by snorkle do you mean the air cleaner manifold assembly ontop of the throttle body ?

My cleaning method was to remove that assembly and expose the throttle body and lock back the throttle cable assembly in order to keep open the plates (butterfly). Then I would clean both top and bottom sides of the plates and also inside the throat and bottom area.  Most recently, I saw that the plates were not open  and flat in place before I replaced the air cleaner assembly after reinstalling the ISC this first time.

 

This morn I had an afterthought:  after removing the ISC this first time, that allowed the throttle cable assembly to move forward (counterclockwise) since the ISC plunger no longer held it back.

Could this have compromised something? I was thinking that perhaps the jerk forward may have done something to the TPS unit. It seems that the throttle cable linkage is connected all the way through to the back of the throttle body and sticks out some in order to engage the inside of the TPS unit.

The inside of the TPS unit (back side) seems to be a round opening with two plastic 'tabs or ears' that are fixed in place and do not rotate. Could these have broken without throwing a TPS code?

(I have a new spare TPS unit as a reference).

Or could it have caused the idle air  adjustment screw to move out of spec?

I guess I am wondering ultimately whether a compromised TPS unit can cause fast, steady idle (1500 RPM) ?

Another question:  What is the full throw distance of the ISC plunger?

With the plunger at the engine off position, and retracting the throttle cable assembly , I can cause the plunger to go back and forth 2/16 inch.

I assume that when I get the idle to 2000 and use finger pressure on the ISC plunger, the plunger should retract alot more. But what is the expected movement distance if the ISC is working correctly?

I have not physically re-tinkered with this '92 Eldo yet. Going to work the other car this morning.

Thanks !

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I didn't read the above yet, but check for vacuum leaks since the top of the intake comes off and that you have had it off.  An unmetered air / vacuum leak will cause it to idle fast.  

When I go to bed later Ill look at the P030 code and see what sets it, if the idle is high due to a vacuum leak and the ISC can not compensate, its possible that the P030 sets. 

I want to remind you to NEVER start the.engine with the plenum cover off as the engine will accelerate uncontrollably.

The O2 sensors can set P042 and P044 lean codes, but I am unsure if a small vacuum leak that increases the idle would trigger them on the OBD1 system.  

I will let others chime in but, if you spray carb cleaner around the possible leak points a change in idle would indicate a leak.

Do you have any other P codes?

@the gold2

 

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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Hi BodybyFisher, thanks for the caution about having the engine on with plenum cover off ! GOOD TO KNOW. Fortunately I have a habit of buttoning stuff up before starting the engine.

It has not thrown any P-Codes in the recent past.

When I had the EGR replaced and reamed, sparks, wires, dist cap replaced and the fuel pressure valve etc.. some 4 yrs ago (to satisfy the smog check and P code), the vac lines at the throttle body were replaced with 'silicone ones', I believe. Since then I have only run about 2000 miles, believe it or not ! Just a fair weather car...

 

Anyway, since I ended up doing brakes then an oil service and radiator service on my other car today, I slipped in a very quick manual test on the Eldo.

Held the throttle cable assembly open to about 2000 RPM (it idles steady at 1500-throws CE Light) and tried to move the ISC plunger backward. I could not do it with one finger. Tried twice. No cigar.

So this trial may have been a  flawed technique on my part but I throw it out there. I did poke around the vac lines at the throttle body and they appeared fine.

 

Thanks again !

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