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Replacing Idle Speed Control Motor Northstar


manowar77

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Hi guys,

when i started up my Northstar today the idle was to high, ant it only kept rising until i shut the engine off!

Checked for codes....no codes appeared!

When i got off work, it ran normally....it was like this about a year ago with a too high idle, since then it have been normal until today!

Last time it was like this, i heard a clicking noise from the throttle body area.....is it time to replace the idle speed control motor?

Is it a hard job to do yourself? Do i also have the replace any gaskets doing that?

Rockauto have one for 49 US dollars!

Cleaning the TB i maybe a good idea to do also, but since it happens only once a year and when i did last time i heard a clicking sound im thinking of the ISC!

So, is it much work to do yourself and do i need any new gaskets etc?

Roger Martinsen

Roger Martinsen

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I have a 1995 STS also and I did my ISC a couple months ago. It wasn't too terribly hard, and I'm a newbie when it comes to working on cars. There's no gasket to replace. A stubby wrench might help to get at one of the nuts, I didn't have a big enough torx driver so I left the ISC bracket on the car and used a stubby wrench to reach the inside nuts.

It clicks and the plunger on the ISC moves when it's looking for the idle settings, and your gas pedal will move in and out. There's a procedure in the FSM to adjust the idle, I don't have my FSM here or I would post it for you (I think it's listed on caddyinfo somewhere). You could try adjusting the idle before you replace it.

Here's a post about taking the ISC motor apart and cleaning it, you could try that as well if you're inclinded: http://caddyinfo.ipbhost.com/index.php?sho...amp;mode=linear

I'm not positive but I don't imagine that the car will run right if you unplug the ISC.

Hope this helps.

WARNING: I'm a total car newbie, don't be surprised if I ask a stupid question! Just trying to learn.

Cheers!

5% discount code at RockAuto.com - click here for your discount!

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I have also replaced the Idle Speed Control Motor (ISCM). It is somewhat difficult because there are three small nuts, which I believe are 5/16-inch, which equates to I believe 8mm. The lower one is a pain to get at because there is very little room. The air box needs to be removed, which is obvious. I remember that I removed the (I believe 13mm) nut that secures the transmission cooler line to the transmission to give me more room to get at the lower ISCM nut. I was able to pull the line off its stud and move it out of the way somewhat. If I remember that line made it more difficult because it didn't allow me the maneuvering room to get the combination wrench on the nut and turn it. Once the line was out of the way it made things a bit more easy. If I were you, I would have a magnetic pickup tool just in case. I didn't adjust mine and it worked fine, but other will say to make sure the gap between the plunger and throttle body is, if I remember correctly, something like sixty-thousands of an inch (.0060).

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Will the engine still work normally if i disconnect the electrical connector to the ISC? Is this possible until i can replace the ISC?

The problem is that the ISC is needed to maintain idle speed. If you disconnect the ISC electrical harness at the wrong time, for example, when the engine is racing at 1500 rpm, that is were it will stay because the plunger will not retract since it's no longer getting an electrical signal. Then again, let's say you unplug the ISC harness when the idle is at 650 rpm, the problem is that in the morning when the engine is cold it will not idle on its own and will likely stall. Once the engine is warmed up to normal operating temp, then you will likely be able to maintain idle, but it will be somewhat erratic even when the engine is warm because the ISC is integral to maintaining proper idling. I know this from personal experience. I disconnected the ISC because the engine was racing. I was able to get the idle to calm down and then pulled the harness. Then I replace the ISC as soon as possible.

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  • 1 month later...

Hello everyone,

I was going to replace ISC but instead i removed it, cleaned it and greased it! It was like MAC said very difficult to gain access to the lower nut, but at the end it came off and i could remove ISC!

Then i took it apart and there wasnt much grease left inside, so i gently brushed it and re-greased it so it would do fine!

Then it was a little pain in the *smurf* get get the lower nut on again, but with a magnetic screwdriver i managed to screw it on the threads at last, after that it was only to reattach the air filter housing and after that i also changed the air filter (It was 3 years since i replaced it,but the old one was as new when i took it up)!

Now the ISC works fine, a little grease was all that it needed!

Roger Martinsen

Sweden

Roger Martinsen

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  • 3 years later...

Ok, I had a similar issue with my 1997 Deville with 4.6 Northstar Engine. My car would idle very rough in the morning and then approx. 20 seconds later after I stepped on the gas a few times it would idle normal. Let it sit for a while and the problem comes back. At first I thought it was the spark plugs and replaced them, didn't help my problem but I car did run a little better. Then I thought I had a sticking injector, so I tested them all with an Ohm Meter by simply unplugging them and using the meter, they all tested out at approx. 24 ohms, so I figured they must be good, but could one be sticking open when the motor shuts down and slowly leaks gas into the cyclinder since the fuel rail is always under pressure? I really thought that was it. Then I thought a little harder about the first days of fuel injection when they were used only on race cars, they did not have idle circuits at that time which meant that normal passenger cars could not run fuel injection. Later they invented an idle circuit for fuel injection and then slowly every car being built had fuel injection, mechanical throttle body type. Anyhow, I decided to take the Idle Control Valve of the throttle body, held in place by two #20 torx screws on the left side. Tried to pull the plunger in and out and it barely cam out and back in but with a lot of force. I pulled it out again and cleaned it up with some PB50 (WD40 or whatever you got) and then applied some grease on the plunger shaft and pushed it in and out a couple times, seemed much better. Then I cleaned out the port that it was in a bit and re-installed it. Now the car runs and IDLES normal. At first it revs up a little high like its supposed to and then quickly settles to a perfect smooth idle. Fixed. You can simply buy a new Idle Control Valve, Rock Auto has them for about $50. I am going to purchase a new one now and replace it when it arrives just to be on the safe side, but at least I did not need it right away because the local auto parts store wants $95 for the same part, so I was able to fix the problem and save some $$. It was a fairly easy job and it costs nothing for you to take it off, check the plunger and reinstall. There is an o-ring on it, so be sure that when you re-install that your o-ring is ok to reuse, mine was fine.

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