Idle Speed Control Motor

What is the purpose of this part?

It controls the idle speed. Sounds like a smartass reply, but it really is that simple. It's got engine coolant going through it, plus it's controlled by the ECM. It allows air to go in around the throttle valve to make sure the idle speed stays at 850. When the coolant is cold, that is the determining factor, more air is let in so that the idle is up around 1,500 or so. When the coolant warms up, the computer takes over. This is why you shouldn't adjust any screws on the throttle body, if your idle is too high, something is wrong, maybe this Idle Speed Control Motor, more likely a vacuum leak.

There is another one, called the A/C Idle Up Controller, mounted on the firewall. That one bumps up the idle a little if the A/C is on. It has a screw on it for adjustment.

How does it get engine coolant into it? As far as I've found it only has a wiring harness hook up. Also what does the lever/ arm covered in the rubber gasket do?

The part I'm talking about is mounted on the throttle body and has two coolant hoses about the size of vacuum hoses going to it. Maybe we're talking about different years or something.

Woodie you got the guy confused, the early metros were using a thermo choke controled by the coolant temperature they do not have ussualy idle speed motors just throtlle possition sensors, the newer ones uses the electronic controled idle motor who is controlled by ECM, based on the reading of the coolant temperature sensor and air intake temperature sensor the ECM applys a voltage to the idle speed motor who in turn opens or closes the butterfly valve of the throtlle body, it is also known as electronic controled choke, when the coolant is cold the ECM send a signal to the idle motor to keep the butterfly valve closed while enriching the mixture of gas by not allowing to much air in, when the coolant is hot or warm viceversa.

On my '95 Metro 3-cylinder with throttle body injection, the Idle Speed Control Motor is an electromechanical assembly mounted to the intake manifold. The only thing it does is opens up the throttle valve when commanded by the ECM. I've verified with my Vetronix scan tool that it does nothing when the engine is cold. Cold engine RPM is controlled by ignition timing and fuel injection alone. The only time the Idle Speed Control motor is actuated is when the gas peddle is not depressed and the air conditioning compressor is on.

Flash, On the earlier metro the valve controls the idle by increasing or decreasing a small amount of air the goes into the TB. The computer sends a signal to the valve depending on such things as elecrical load (turn on your headlights at idle the idle will go down but the vavle will compensate by letting some more air bypass into the TB). If the valve goes bad, it will allow to much air to go into the TB causing a high idle.

Don't confuse this valve with the valve built into the TB that opens and closes with cooland temp. That valve has a wax matrix that expands as the engine warms. If you look into the carb you see a hole on the backside. As the wax matrix expands, it cuts of air entering that hole. When coolant is cold you need that extra air to keep the idle high as the engine warms you need less bypass air. THIS IS A DIFFERENT VALVE THAN THE ISC VALVE that I posted pictures earlier.




Did you plug the line that goes from the valve to the lower TB? What did you idle do?

This is only one of many things that can cause a high idel. First check to see if you have a vacuum leak. Use carb cleaner. When the cleaner hits a leak, the car will idle down.

If no leaks and all the hoses are not cracked and attached per underhood diagram, then you should try and use the idle screw on the side of TB to try and lower the idle by turning the screw in. If the screw is all the way in and you still have high idle, back the screw out and check for a bad isc valve.

Plug the hose from gthe valve to the TB and tell us what happens? I have had these go out in both of my metros.

Here is a thread where I talk about the ISC vavle and the cold start vavle built into the TB. my isues was the ISC. PICTURES INCLUDED

http://www.teamswift.net/viewtopic.php?f=5&t=25522&hilit=valve

one last thing. There are two idle scews, do not mess with the one that is in the linkage that has a black plastic cap from the factory and should never be removed. The other idle screw has a rubber cap covering it. It goes into the TB itself. That is the one that you can adjust. If the cap is missing on the former one, someone might have been playing with it. Another memeber on this form was having issues with his idle and turned out that the previous owner had messed with the scew that was not suppose to be messed with.

Guys, I went through six pages on this forum to find the info. you are talking about. I have learned a lot. My problem is a little different. On my 1994 Metro, I can adjust the idle speed manually to compensate for the air conditioner being on, but when I turn the air off, it idles way too high. Do you think my ISC is defective, or is it not getting the signal from the computer?

What are you adjusting to increase you idle?


The ac system has a seperate valve that boosts the idle when ac is on.

It is on the firewall upper right center of this pic
http://img.photobucket.com/albums/v489/RossT/Image059-1.jpg

Does your isc valve look like the ones in the teamswift link above that I posted?

http://img.photobucket.com/albums/v489/RossT/Image005.jpg

If so then you make the idle ajustment on the TB itself (don't touch the one on the linkage)



Make sure your car is timed properly too.

Ross, I appreciate your response. However, the Hanes manual states that on late 1994 models the emissions system was upgraded allowing the ECU to control the idel speed with the ISC motor mounted on the back side of the throttle body. The emissions info tag under the hood verifies this. This model does not have an AC valve on the firewall, nor does it have an ISC valve like the ones you showed.

At the base of the throttle body assy., there is a traditional idle adjustment screw. I have set this so the engine idles at the proper RPM's with the air conditioner turned off. It should rev when the air is turned on, but it does not. The "plunger" on the ISC motor (a Denso PN 161100-0050 if you are interested) doesn't move under any conditions. This is why I thought it might be defective.

That is why I posted the pics of the ac valve and isc valve. I was trying to figure out what type of system you had on your 94.

You can try to remove and clean you idle valve to may sure that it opens and closes properly with signal from the ecm. From what I have seen, on the new metros, when these go bad, the car will have a hard time idling, while on the older metros, the idle goes sky high when the isc goes bad.

Sorry I couldn't help further..