I'm trouble shooting a high idle problem on my '87 420. I've cleaned the ICV before but this time I put 12v on it just to make sure it works. I see that with 12v on it, the valve does move up about 50% but it does not move up to the complete top to shut off air flow completely. Is this how the valve is supposed to work? Is there always a space left to let some air in?


Thanks

I believe valve should close completely and stall the engine. If it will not close off completely, it may be dirty with cqarbon build up. Suggest you remove it and carefully clean it with a carbon removing spray. Be careful, these sprays are highly combustible.

Thanks for the response BFGW.

I've cleaned the ICV several times in the past soaking it in carb cleaner. Funny thing was in the past the ICV was causing a rough idle and after cleaning, the idle smoothed out. But now, a high idle problem started a few weeks ago, 1700 in P and about 1100 in D. Now it seems I'm getting too much air through the ICV instead of not enough. I put a meter on the ICV and was getting between 3-5 volts when the engine was running, so I believe its getting enough power to operate properly when it is connected. And when I disconnected the ICV, the idle would surge another 300rpms.
Also disconnecting the TPS caused a surge in the idle. The only test that failed was when I turned on the A/C to max, the idle dropped about 300rpms indicating according to posts, that maybe the ICU was not working properly.
The OVP fuse is good and contacts are good. Pulled the ICU and it looked good. Nothing on there looked fried but did not take a magnifiying glass to examine the solder points.

So, I wanted to see how the idle would behave if I were to restrict airflow more than my ICV is currenlty able to do, so I used a trick I had read about on this site. I cut a quarter inch slice of broom handle and drilled a 4mm hole in the center and put it in one of the hoses on the ICV to restrict air flow. The car idle dropped to a smooth 500rpms. THe car has NEVER idled at 500 since I've had it. With the broom handle piece in the place, disconnecting the ICV caused an increase in idle to about 750, as did disconnecting the TPS. And suprisingly, when I turned the A/C on to max, the idle did not drop at all and stayed at 500.

So now, I'm wondering if I should just drive my car with a piece of broom handle in the engine or replace the ICV? But would still appreciate some more input regarding how far the ICV should close during normal operation before I deduce that in need a new ICV.

Thanks.

After cleaning the valve, I got the car to idle OK for a number of months. almost a yeat. Eventually, the idle again became erratic, sometimes high to start with, then when the car was good and hot (south Florida summer), itwould drop to normal. After trying everything / testing everything, I finnaly bought a rebuilt idle controller module. Problem solved!