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erratic cold idle

1200 Views 8 Replies 4 Participants Last post by  CorseChris
My 24v QV hunts to the point of stalling in the first 1.5 -2 minutes from cold start. After that it settles down and has no further problems. It has just had the cams retimed. Idle control valve? It settles so quickly nothing much can have heated up.
Any suggestions?
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Motronic temp sensor or a bad vacume leak? Is the computer throwing you out any codes of any type? Maybe give all the connectors and grounds a good cleaning, then see what happens, best of luck,

well, today my L did erratic idle at cold start all of a sudden. As usual I started up the car, it did start up and then the idle stayed at 2Krpms for about 2min while the engine ran fine while driving, but as soon as I disengage the clutch they went up to 2Krpms for that 2min. Now its running fine again.

Now having stalling problems too - there doesn't seem to be any detectable voltages at the IACV plug - does anybody know what sort of voltage/signal the three pins should carry?
There should be a solid 12V on pin 2, then some flavour of square wave drive on pins 1 & 3, depending on demanded IACV position....but I've never looked at the drive on the 3 wire valve so can't do anything but guess.....but I'd expect it to be balancing between the two, so for example, if pin 1 had almost 100% low, pin 3 would be almost 100% high, and vice versa. IYSWIM. Trying to measure this with a voltmeter would be awkward, but it might tend to average it again guessing...look for something like average 3V on one pin and average 9v on the other, not forgetting, it'll be changing all the while as it controls idle. A 'scope would be better....

One of the pins is connected to the shielding wire of the cable - presume that'll be an earth. Would that make the three +12v, earth and signal?
Mmmm. Don't sound quite right that......the 3-wire IACV has 12V on pin 2 (the centre pin) and pins 1 & 3 go to the ECU, both are active-low drives, ECU pins 2 & 29 (I think - poor copy of the ML 1.7 diagram). Wouldn't expect them to use a screen for a drive line.

Are you sure it's the IACV plug you've got there? Sounds more like the CAS if it's got a screen connection??? there's a thought....did they put the plugs back on wrong after timing the cams?

Or check the colour codes. According to the diagram I'm looking at anyway...

1 Orange/Black
2 Orange/White
3 Blue/Black


1 Red
2 White
3 Screen

Only 3 way plugs with screens on are CPS, CAS, Knock sensor x 2 Could the cam angle sensor be the one? Don't even know if they are keyed at all I'm afraid.

I'm clutching at straws here!!
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Well Chris, your first post got me scuttling for the wiring diagrams too. The IACV and a knock sensor cables had been swapped when the engine was last installed! (not by me) Now starts on the button and idles the way I remember it! Phew!
Excellent. Looking at the diagram, I reckon no harm will have been done to the knock sensor or anything else due to that swap, so should all be good to go.
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