So my car has been developing an idling problem over the last 6 months or so and i'm just trying to figure out what's causing it. I went through old posts and decided i need to clean my ISV. Did this and it has no effect. The engine will fall on it's face and stall if i don't blip the throttle a whole bunch when coming to a stop or just trying to idle, anytime. I'm wondering does the ISV recieve a signal from the throttle swith telling it when to open? If so maybe i need a look there. There are no vaccum leaks and most of those hoses have been replaced. One more quick thing, there's a plug near the ISV with nothing plugged into it. Three wires, two blue and black and i think one red. Anyone know what that goes to? Thought and suggestions otherwise?

Thanks
Jeff

 

Airflow passes thru the MAF (metered air) and enters the intake manifold at the point where the "Michelin Man" hose connects to the intercooler. If you remove the MM hose you will see the throttle plate and a cast air channel which allows air to bypass the closed (at idle) throttle plate and enter the other end of the intake manifold via the ISV. This is why the MM hose has the tear drop shape.

With the throttle plate closed (foot off the gas) the throttle switch directs the ISV controller (marked as Idle Volume Control on my fuse panel, gotta love the translation) to regulate air flow into the intake manifold using the ISV. The ISV contains an air regulator disk controlled by a solenoid. With current applied to the solenoid the disk will move toward the electrical connector providing a path for air to enter the intake manifold. With no power applied a return spring returns the disk to the shut position.

It was suggested that a vacuum leak could cause the problem. It was not clear to me how a leak could cause the engine rpm to increase. It seemed that the increase in rpm was likely due to an increase in metered air and the engine computer was responding accordingly. I felt a vacuum leak would cause unmetered air to enter the intake manifold resulting in an idle stumble.

As suggested I cleaned the ISV and then tested it with a 12 volt/half amp power supply. The disk moved freely and snapped shut when power was removed. One notable difference was that the replacement ISV would not pass air when I blew into the inlet side of the ISV. The problem ISV would allow air to pass.

I replaced the ISV with a used one from Force 5.

The throttle switch will make a clicking noise when the plate closes. It's a good sign if it clicks but not enough in itself. You can measure for continuity by removing the connector.

I don't know what the extra connector is for.

 

I have those wires also. I got really worried because there is also a bracket similar to the one that holds my hydraulic fluid, so I investigated a little further. I don't know what kind of car you have, but I have a 1990 200 TQ and my buddy has an 87 5000. I was comparing our engines and found that he actually has a windshield washer fluid reservoir behind his ISV. Mine is tucked away in the lower left corner of the engine area, next to the airbox. So I don't know if the previous owners changed this or what.

 

mine's an 875KTQ and has the washer fluid behind the ISV as well.

 

high throttle.