Has my ECU died?

Discussion in 'Engine' started by gt-83, Jun 18, 2011.

  1. gt-83

    gt-83 Active Member

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    the idle control valve on my 260e keeps opening and shutting causing the engine to surge, its not the valve as i have now tried three of them to cure the problem, and i can see whats happening by plugging in a valve not attached to the engine, looking at the wiring diagram, the two wires that operate it go to the ovp relay and the ke control unit, as the fuses are ok on the ovp relay does this mean my ecu is knackered, ......the car runs ok with the icv disconnected.......any w124 experts?
     
  2. grober

    grober MB Master

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    The OVP relay supplies the idle control valve with 12V and the current operating it is controlled by the ECU switching this to ground at a certain rate. Check the OVP is supplying a stable 12v under load. It's possible the OVP is faulty [ burnt contacts] You could try testing the OVP by simply supplying a temporary 12v supply from the battery. If this cures it it's probably the OVP. If not its the ECU
    That's the electrical side erratic idling is often caused by airleaks in the inlet manifold or associated rubber pipe work. The idle control valve may be operating correctly but the mixture is outside the normal control parameters causing it cycle?
     
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  3. OP
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    gt-83

    gt-83 Active Member

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    thanks for a detailed reply, that should enable me to eliminate one or the other, did you mean a 12v supply direct to the icv?, i did actually put a meter across the supply and it was giving a constant 12v!
     
  4. grober

    grober MB Master

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    Yep a substitute 12V direct to the ICV supply connector instead of from the OVP Its possible the 12V will only drop under current drain due to poor contacts in the OVP.
     
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    gt-83

    gt-83 Active Member

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    Now im really confused, up early and into the garage to sort this problem, with a supply direct from the battery, the valve opens and causes the engine to surge (1500revs) constantly, take away the supply and she idles nicely (all the valves i have do this), with the plug in (normal supply) it surges then idles, surges then idles, and so on.
     
  6. OP
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    gt-83

    gt-83 Active Member

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    can i assume that as 12v direct makes the valve open constantly and when the normal supply is plugged in its erratic, the ecu controlling the power has the problem, idles nicely without icv plugged in, so this must rule out air leaks.

    i think ive just answered my initial question:(
     
  7. grober

    grober MB Master

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    Assuming you got the connections correct it would appear the ECU is not switching to ground to control the valve and the idle is cycling due to other factors mixture control etc. The zero switching to ground may be a faulty ECU or the control might be effected by 2 other parameters that effect the ECU namely the engine coolant temperature sensor and air conditioning load [ if you have air con] causing the idle control to "switch off" The other thing that I wondered about are there any throttle limit switches which tell the ECU the car is in idle state? i.e. no throttle open--- don't know where these are on your system and exactly what the consequences of a faulty/disconnected limit switch might be but that's another possibility. And check all that vacuum/inlet flexible pipework for leaks also.
     
  8. OP
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    gt-83

    gt-83 Active Member

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    Graeme, thanks for sticking with me on my problem, i have checked the throttle switch and it is working fine, i did wonder about the coolant sensor, unplugged it with no difference (but then there wouldnt be if it were faulty!),

    i will try some easy start or similar to see if there are any leaks, though i have inspected everything.
     
  9. grober

    grober MB Master

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    Hope the problem is resolved soon. I am always reluctant to blame the ECU since many problems are down to switches/sensors rather then the central unit- but things do seem to be pointing in that direction. It might be worth asking on the 190 forum since they have similar injection systems. Mercedes-190.co.uk and someone there may have experienced a similar problem?
     
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