Cold Fast Idle

landrovernuts · Post by **landrovernuts** » Wed Dec 18, 2013 7:40 am

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 10 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! I put this on one of the Land Rover for forums, but there was silence.

Toby

unstable load · Post by **unstable load** » Wed Dec 18, 2013 11:59 am

Temp probe/switch in the circuit, maybe?

ChrisJC · Post by **ChrisJC** » Wed Dec 18, 2013 7:05 pm

Can you continuity test the wires between the ECU and the stepper?

Chris.

landrovernuts · Post by **landrovernuts** » Thu Dec 19, 2013 1:58 pm

That was my next plan of attack - but will need to wait until the rain stops!

DEVONMAN · Post by **DEVONMAN** » Thu Dec 19, 2013 6:36 pm

Also check the wires to the coolant temp sensor.
Unlikely , but if it shorts to earth then the ECU will think the engine is hot.

Denis