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MG MGF Technical - mgf vvc revs not returning to idle

Hi everyone.
This is my first time on this forum so I'm hoping I do it justice.
The problem i have is the revs won't return to idle speed (850-900)every time and i have to resort to blipping the throttle frequently.The head gasket was recently replaced (the problem was not there beforehand)but the engineer who did the job is very experienced and he has checked or replaced all sensors and thought the problem was sorted by replacing the coil pack ( the car ran well for the 140 miles home) but the next day the idle problem arose again and eventually you have too do a tps reset to get the idle speed correct.The throttle butterfly does not appear to be sticking as if you rev the engine by moving the cam it returns back straight away.
Does anyone know how to check for correct sensor operation ie resistance of coolant sensor,tps and iacv etc and/or have any ideas as to the problem as I'm now beginning to tear my hair out and it's costing me a fortune. Many thanks steve
s marine

An archive search here or on the F register might give you some useful angles.
If you are after the sensor resistances and have a decent meter, log on to Dieter's website http://www.mgfcar.de/
and look under 'sensoren'
Charless

Just add /sensor to the domain.
:)
http://www.mgfcar.de/sensor

Might be a problem with the connectors. Either at the sensors or direct at the ECU.
Similar troubles came up frequently in the last few month.

In case you feel yourself able to check this acccording to your technical skills:
Disconnect the black ECU connector and remove the large red coloured silicon like gasket from the connector. Just for a test, this will provide some mils improved connection length.

Try if this solves the problem. If not, then put back the gasket.
If it's OK suddenly then you can put it down to any troubles at the ECU connector.
Finally I'd not recommend to leave out the seal for a longer time due to humidity to the connection pins.

Next to test would be the engine wiring loom itself for brocken or corroded wires. Special the thin wires to the sensors.
Dieter

thanks Charless and Dieter. Will try and work thro the sensors one by one .Very valuable info..Many thanks again steve
s marine

There is a useful article in another forum.
http://www.the-t-bar.com/en/forum/21-aiketgates-guides/17678-iac-valve-how-to-remove-and-refit

Jeff
J Lennon

There is a valve that gets a bit clogged just by the rear of the rocker cover, stepper motor. Give it a clean.
You can also try this

the throttle body has been recently replaced, or you find that the idle speed is a little on the high side, it may be worth attempting to reset the throttle position sensor (TPS). This is readily achieved by following the following procedure:

Start engine and warm engine to its normal operating temperature (essential, as when cold, the engine requires some extra air/fuel - which on the MGF is managed by the idle air control valve: best not confuse the issue!)
Now turn off the ignition.
Switch on the ignition to position II without starting the engine (all the pre-start warning lights ought to be illuminated)
Depress the throttle pedal to the carpet and fully release inside a period of 30 seconds or so.
Wait for about 15 seconds...
Switch off the ignition
The engine can now be re-started; the TPS has been re-set
Andrew Regens

steve got to the root of the problem and fixed it. details below for anyone finding this in the archives!

"Have just finally come across an easy,cheap fix for the all too common sticking throttle body,whereby the revs don't return back to idle.
Assuming that alls well with the idle control valve and TPS, gaskets etc etc, simply by adding an extra torsional spring from the TB cam to the clip (holding pipe)just above gives that extra bit of closure on the butterfly which is all that is needed at times.
Whilst the extra spring is virtually un-noticeable on the accelerator pedal that extra little bit has cured my annoying errattic idle return problem.
Whilst i can't guarantee it will fix anyone else's problems it is at least a cheap option worth considering." Steve M
Leigh Reid

This thread was discussed between 27/06/2011 and 17/07/2011

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