>>The Idle Speed Motor does a fine job of setting the idle speed, and of maintaing it. But as I found on my car, only when you drive gently.<< Thenn something is wrong with your car and you've compensated for it by using the manual idle. >>If the engine is at a high rev (usually about 4K or more RPMs), then when you push the clutch in to drop (or let off the gas on an auto from my experience), the RPMs will fall VERY quickly.<< The CIS has nothing to do with this. Again, you have other problems. I suggest you check your decel valves or throttle linkage setup. My car (an auto) experiences none of these problems. >>Now I had to compensate on my car to bend the bracket for the Idle Speed Microswitch, and extending the stop bolt on the throttle assembly. This now causes my Idle Speed Circuit to trip early, and activate the ICM so that it will open early enough so the engine doesn't dip too low, and I keep my electrical system stable.<< Again, you need to find ths source of the orignal problem, not bend things to fix it. How many other owners have had to do what you've done? >>However, there has of course been a trade off. I now have no gradual powerband. Gently pressing my acellerator pedal, The ISM then tries to compensate for a "fast idle" by choking my engine, rather than allowing me to add the extra airflow to my acelleration. Once the Microswitch is deactivated, my RPMs then jump to 1,500!<< You clearly have something way out of whack and you're going about fixing it the wrong way. Also, your statments imply you don't have a full grasp of how the CIS system operates. >>The other problem with the Idle Speed Circuit is that it doesn't like to work well with a motor that's not properly tuned. If you do have a vaccum leak, or you're running rich, then the idle seeking/hunting will of course occur (that's the LAMBDA system cycling).<< Well, you need to tune your engine. And I said the engine must be in good health with the CO set properly. The Lambda will cause a very minor idle hunt of less than 50 rpms if everything is setup correctly, or none at all if you chose to set it another way. All the symptoms you described indicate other problems, your car should do *none* of those things. >>However, I do feel that as great of a system that it is, that it needs to be supplemented.<< Absolutely incorrect. It will perform flawlessly if set up properly, as long as the engine has no major problems. I have mass flow measured the CIS system know this to be true. >By setting the initial Engine Idle Speed manually with the 3 brass screws, we create a "pillow" of sorts for the engine speed. The idle should stay far more stable.< Yes, thats true (see below) but you're not setting it up correctly if you use the brass screw to do that. It will work however but you shouldn't be using the balancing screws at all. >When the RPMs drop hard, the engine isn't going to have to wait for the ISM to activate, and open up to feed the engine air.< The CIS valve sets to it's basic position as soon as you turn the ignition on, before you start the engine, as long as the idle switch is made. It only beccomes closed loop after ignition/tach impulses arrive. >>Now, if there is any downside to utilizing the Manual portion of the Idle Speed Circuit, then please, let me know. I myself really don't see any harm in using it. Only benefit.<< No harm but as you say, you shouldn't need to do it. There is no benefit to setting idle speed manually. It has no "improvement" over a properly tuned CIS. You clearly have problems with your car. >>>If you will follow the link to the web site, it will show you how to set the idle. I would set it 950. 775 is to low. About middle of the page.<< John, your procedure is ok for manual idle but useless for CIS. Again, you're chossing to set idle speed manually because of an inability to correct for CIS problems. Sure, setting the idle manually as you state can be done and 950 is fine for open loop control. You will lose the benefits of closed loop control however. As for 775 being to low, this setpoint is hardware built into the CIS ECU and can only be altered by a component change. We're talking apples to oranges, I'm talking about making the CIS work as it should in full close loop. It *will* do this if set up correctly. But I'll agree a higher idle is beneficial at times. My ECU has been modified to increase idle rpm to 950 when the headlights, A/C or cooling fans are on. I see I'm dealing with shadetree mechanics and not engineers. The point I'm making is to stop viewing this as a car part, the CIS is a simple flow control loop. If you want a decent idle (assuming the engine is in good health and your CO is set properly) you need to prevent the CIS from controlling *all* the air that enters the engine. CIS conductance is not effected by CPR control pressure and that makes a big difference in mixture management. By allowing the CIS to control all the air entering after the throttle body you increase it's response (it's proportinal band, for those of you who understand control theory) and this canlead to oscillation. By allowing it to control a window around metered air you decrease it's response to overshoot. Even the Volvo and Bosch CIS setup procedures make this clear and it makes perfect sense. It's why you set manual idle *higher* during setup than the CIS provided setpoint. It's difficult to adjust or troubleshoot a feedback loop of any kind when it's closed, thats why you need to open it for setup. If you want to remove or plug the CIS path into the engine then yes, you can use the brass idle set screw on the throttle body to set idle speed. But if you prefer to leave the system in place a better way is to force the CIS motor to it's default position. This is done by removing the rpm input to the CIS ECU. The idle speed can then be set by using the throttle plate stop screw while still allowing the CIS motor valve to return to it's basic position whenever the throttle is closed. It leaves the CIS system intact, albiet not closed loop active. Either method is effective and either will give you a stable manual idle, as will correct setup of the CIS. Why people disconnect the system is beyond me, there are no benefits other than to hide the root cause of problems. I can spout all the theory on Earth but this isn't rocket science. It's your choice to run your car anyway you wish, I offer this only from a desire to demystify the CIS system and rebuke the long held notion it doesn't work as designed. If your car hunts during idle it shouldn't...period. Course, what do I know. Like I said, my D idles and runs perfectly in all regimes and so does the other one I maintain for a friend. And what is all this I keep reading about vacuum leaks caused by bad valve cover gaskets? There is no negative pressure with regard to ambient under the valve covers, on the contrary...measure it and you'll see.