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MG MGF Technical - ECT sensor fault? fan on & fast idle

Quick question, having checked the archives and read the manual I am still not 100% sure I have this right.

1996 VVC. No aircon.
High idle around 1500rpm, occasionally it will drop if you tap the accel. pedal when stationary but it then climbs again. Tried the stepper reset a few times to no avail. Engine fan also always on.
I suspect it is the ECT sensor (yes, the brown thing front left side of the engine block )

If the ECT sensor is dodgy will this cause the fan to always be on and also raise the idle speed? Mine sits at 1500rpm at present ie seems to be in warmup mode. Seems an odd default mode as it covers both cold engine/hot engine scenarios.

I want to check before I go getting at the engine, however would it be worth a quick check & cleanup of the connecters?
thank
Charlie
Charles Dundas

Yes, definitely worth a dose of electrical contact spray on the brown sensor connectors before declaring the sensor duff, but those are the classic symptoms of a failed sensor, when the ECU isn't getting a coolant temperature reading it assumes a stone-cold engine but runs the fan as a failsafe precaution.
bandit

Thanks, I will get some spray and give it a go today.
Charles Dundas

try this with a multimeter set to DC volts, I use a couple of bits of mig welding wire pushed in to the back of the plug to get a connection for the meter.

Alex Sturgeon

Hi
I have the same problem with my mgf its gotten worse every time someone tries to fix it it used to idle at 1500 to 2000 rpm fan cuts in all the time now its ideling at 3000 rpm not fixed could you tell me if the ect sensor worked
regards
keith
keith massey

well, car has been in storage for 12 months: just changed the rear brake pads but after changing the sensor it is still idling at 150o.
Old sensor was ok (tried it by measuring the resistance in a cup of hot water) and the wiring is ok from sensor to MEMS black plug.

Where to from here?
Charles Dundas

This thread was discussed between 20/10/2008 and 22/03/2010

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