Date: Mon, 15 Apr 2002 23:00:07 GMT From: Bob <uctraingLOWSPAMnopsamanet.com> Subject: Re: 98 Vibration - Front End
On Sat, 13 Apr 2002 09:13:12 -0400, "B. Smith" <b.smithnopsamco.ca> wrote: >Reprogramming the ECU makes a lot of sense. How does one go about getting >this done or acquiring the programming that is currently there? This is a rather complicated job and is typically done only by folks who are selling performance oriented ECU upgrades. Typical prices are in the $500-$1000 range. How fast is your idle ? The specs say 900 +/-50rpm. I highly recommend a subscription to all AlldataDIY to get detailed info on subjects like the idle control system. Evidently the computer uses the IAC valve to control idle for things like shifting an auto into gear or the A/C switching on. However, the specs note that the ignition *timing* is used to maintain the idle under all other conditions since the IAC control cannot react fast enough: "The engine control module is programmed to maintain engine idling speed at 900 ±50 rpm. Rapid changes in idling speed cannot be compensated for by changing the flow of air. Instead, ignition timing at idling speed is so arranged that engine speed is maintained constant." Bob "Idling speed is controlled via a single-coil Idle Air Control (IAC) valve on the basis of a PWM voltage from the engine control module. Automatic idle speed control is adaptive, i.e. it adapts continuously to changes that take place during the life of the engine. These changes may be wear in the engine, dirt or leaks in the intake manifold or throttle body. The engine control module is programmed to maintain idling speed constant at 900±50 rpm when the engine is warmed up at the same time as the throttle position sensor indicates idle speed. Engine speed compensation takes place when A/C is switched on and when a gear position other than P or N is selected on cars with automatic transmission. When the accelerator pedal is not activated and the throttle is closed, the engine only receives air via the idle air control valve. The ECM controls the degree of opening in the valve to keep idling speed constant. This means for example that the valve opens slightly more when the A/C compressor is switched on or if DRIVE has been selected, in order to compensate the idling speed, which would otherwise fall. The idle air control valve is of single coil type and supplied with power from the main relay. It is controlled from pin 49 of the control module by PWM at a frequency of 500 Hz . The valve opens more the longer the control module keeps pin 49 grounded. The engine control module is programmed to maintain engine idling speed at 900 ±50 rpm. Rapid changes in idling speed cannot be compensated for by changing the flow of air. Instead, ignition timing at idling speed is so arranged that engine speed is maintained constant. If there is an open circuit to the idle air control valve, the opening in the valve is set by a spring so that the idling speed is at least 1000 rpm when the engine is warmed up".
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