I am going out on a limb here by saying this, (it may only be 99% true) but every electronic fuel injected engine ever put in a passenger car has some kind of idle air control valve with the exception of the newer vehicles with "throttle by wire", meaning there is no throttle cable. Instead there is a stepper motor that opens the throttle butterfly, for both idle speed control and cruise control functions thus eliminating quite a few parts.
If you look inside the throttle body, before the throttle plate you will see the "bypass hole". It is the only abnormality you will notice when you look in there. The idle air control valve (AIS motor as Chrysler used to call it) varies how much air can pass through that bypass hole, thus choking the engine just right to achieve the idle speed that the engine computer thinks it should be at. The control valve itself is made of a stepper motor which extends and retracts a pintle-style "gate valve" for lack of better terms. With stepper motor controls, the various coils inside it are energized in specific sequences to make it turn clockwise or counterclockwise. The engine computer has no way to know exactly what position the idle speed motor is in--if it wants to decrease idle speed, it energizes the coils in one order to open it, and the reverse order to open it. Hence the need to "home" stepper motors when working with industrial equipment. Homing is done by inducing rotation (or trying to) one way for several revolutions, even if it has stopped, in order to know that the stepper motor is at its maximum range. It can then start the sequence the other way until it gets the idle speed that the computer wants, and so on... it'd take me a long time to explain it in better Layman's terms than that. Bottom line is that in a perfect world, the engine computer should learn this in a very short amount of time, but if that valve is sticking, or just weak (bad) it will command it to close, and it won't close, so it'll go goofy and not know what to do. I cannot recall exactly how it is achieved with the Chrysler 3.5L engine... because I'm starting to get old and it is late. On the 1st generation 3.5's, there are dual throttle bodies. I think that only one of the throttle bodies has a throttle position sensor and idle air control valve. There are two items screwed to the throttle body that have wires going to them. 1 is the throttle position sensor, and the other is the idle air control valve. > If I understand you correctly this valve allows additional air into > the intake when necessary to keep the RPM's where they should be. > Is that correct? Exactly. I am unsure of proper testing procedures, but in the case of this other guy with the high idle, keep in mind that idle air control valve operation is affected by throttle position sensor voltage to the engine computer. A faulty throttle position sensor can definitely cause that high idle issue.. or I've even seen a car's interior carpet interfering with the throttle cable, or even carbon buildup can keep the plate from closing all the way. Sorry to cut short, but I have to go to bed. ------------------------------------ Web: <http://groups.yahoo.com/group/dodge_intrepid> Subscribe: <mailto://[email protected]> Unsubscribe: <mailto://[email protected]> Moderator: <mailto://[email protected]>Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/dodge_intrepid/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/dodge_intrepid/join (Yahoo! ID required) <*> To change settings via email: mailto:[email protected] mailto:[email protected] <*> To unsubscribe from this group, send an email to: [email protected] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
