Landrovernuts Posted December 14, 2013 Share Posted December 14, 2013 Recently, the fast idle on my 4.2 V8 (hotwire) has stopped working and it tries to idle at about 600 rpm when cold. It used to idle about 1100 rpm until it warmed up then drop back to about 850-900 rmp which was good. Seems to be a bit of a pig now until warmed up, but am putting that down to tthe slow idle. Not that it makes any differance but it is fitted in a 90 and has been fine for the last 7 years and prior to that was fine in a RR classic for 15 years other than routine stepper motor changes!. It would seem at the moment nothing is telling the stepper motor to increase the revs when cold. I know the stepper motor is working as it controls the idle when warm and you can see it dropping the revs back in increments when returning to idle. Just to be sure I have tried a known good stepper motor and it does the same. I have put my stepper motor into another engine and it is fine, so confident we can rule this out. I have changed the coolant sensor for one that I have tested and gives the resistance values as per the Landrover manual and that still has not fixed it. Would the fuel temperature sensor cause this fault? Tried disconnecting ECU power for about minutes to reset it. Next thing I was going to try is changing the ECU for another I have, but do not want to leave them changed as the current ECU is chipped and set up for my engine and the other I have is from a 3.5 hotwire discovery. Anyone got any other ideas before I go hunting for my other ECU? Nothing else seems wrong and even the MPG does not appear to be too bad (for a V8!!!). Just gone through an emmisions test with flying colours also. Any suggestions gratefully received! Toby Quote Link to comment Share on other sites More sharing options...
Landrovernuts Posted December 18, 2013 Author Share Posted December 18, 2013 Swapped ECU - no improvement, then I swapped fuel temperature sensor and that still has made no difference. Anyone have any other ideas? Toby Quote Link to comment Share on other sites More sharing options...
zardos Posted December 18, 2013 Share Posted December 18, 2013 Checked the coolant sensor wiring from ECU to sensor, if it has shorted to earth it might give a very low resistance thus think it is very warm. Quote Link to comment Share on other sites More sharing options...
Landrovernuts Posted December 18, 2013 Author Share Posted December 18, 2013 Thanks - as soon as it stops pouring with rain, I will check. I did notice when I took it for a run that it seemed to run much better and smoother on the 3.5 hotwire ECU than the 4.2 one that was set up for this engine! Toby Quote Link to comment Share on other sites More sharing options...
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