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Old 03-26-2000, 01:58 PM
stevebfl stevebfl is offline
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Sure is a lot to cover. Most of which has recently been discussed.

The idle valve controls rpm all the time not just at certain temps. It has different set values due to temp. All of your readings indicate an uncontrolled idle. The proper tool for monitoring this is a multimeter in the amps position mounted in series with the circuit. Proper warm values should be about 600ma. One good test is to turn on A/C, it should increase the current by 50ma from where ever it was.

If your current readings seem to be unrelated to engine speed you must verify the throttle switch, air flow potentiometer, and possibly a decel switch (not on early models).

The idle of course is a reflection of all the other fuel control functions. On your euro model as with US models fuel control is effected by changing the differential pressure (between upper and lower chambers in the fuel distributor). This is done by opening a controled leak with more or less current flowing through the EHA (electro hydraulic actuator). This signal varies on the different KE systems. Pre 1988 190s use only positive current. After 88 and all 6 and V8 motors use plus and minus current for greater control and better limp home characteristics.

The reason for the better limp home comes from the default position (no forms of enrichment engaged). The plus/minus systems default to zero with the ability to go plus or minus for control. The early 190s use 8ma as the default possition, with the ability to drop to zero or add to whatever. Naturally if your default is zero and you loose control the same result is in effect. If your default is 8ma and you loose control you in effect get a -8ma lean correction.

From the default position there are a number of enrichment corrections. Most systems go to around 20ma with KOEO (key on engine off). Most get 40-60ma starting enrichment (when starter is engaged only). All get cold engine enrichment 0-30+ma depending on temp. Acceleration enrichment (determined by rate of change of air flowmeter potentiometer) 0-10ma. Barometer and feedback lambda control through O2 sensor exhaust monitoring round out the control for US cars. The lambda correction for zero default cars is from -10+ma to +10+ma. On 8ma default systems control is from 0 to around 16ma.

Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

[This message has been edited by stevebfl (edited 03-26-2000).]
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