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MG MGF Technical - High Revs when stopped

Last week whilst driving down to Dover I took the detour through Bracknell to the M3. Having driven down the M4 at 3500-4000 revs without any trouble, the engine revs would not drop below 1500 when I had to stop for traffic/lights etc. Arrival Dover and 1/2 hour later the revs had dropped back to normal at tick over.
Anybody got any ideas as to why the revs would not drop but then settle down when the engine had cooled. I hav'nt had this problem since although the engine bay fan does seem to come more oftern than it used to.
James Forbes Simpson

Two options.

A. sticky throttle butterfly due to dry(squeaking) rubber seal on the butterfly shaft.
Get new metal TB or dismantle and grease with Silicon grease.

B. troubles with ECU connection to any of the 4 sensors. Almost known bad contacts to the TPS (throttle position sensor) or Coolant Temperature Sensor. (brown coloured)

Had and still have case B and need to rattle the wiring harness at the ECU *from time to time* to solve it.

HTH
Dieter
Dieter K.

Hi,

James, my F does this occasionally. Sometimes I can 'cure' it by blipping the throttle, sometimes not. By the time I get to the next idle session it has returned to the usual sub-1k or so.

As fixing it would probably involve expense, someone bodging the car who knows less about the job than I do, the likelihood that some other error is produced, and the even more likelihood that anything they touch will never fit back properly afterwards, I've decided to live with it.

Regards, Kes.
Kes

Good point with the other error producing :)
Decided for the same, but ... anyway I'm always sowhat of curious :)))

Stage 0
Reset sensors with keying the accelerator pedal 5 times. (while ignition on and engine out)

Stage 1.
Changed the throttle body, dismantled the old ... and found the mentioned rubber quad ring _dry_ and responsible for sticky shaft.
http://www.mgfcar.de/throttle/brass_cp_0454.jpg

Stage 2.
Changed the Coolant Temperature Sensor.
Investigated and found the old well working and not broken. (Other here found the same, .. Rob?)

Stage 3.
Found the ECU harness loose near the ECU connector and applying _pull force_ on some of the wires/ECU spade connectors.
Re-tightened and put the individual wires in smooth curves.
*Troubles fixed for a couple of Month*
http://www.mgfcar.de/mems1.9/rivet_Dsc02523.jpg

All sensors get fed with ground at one wire only to the ECU. If this wire has unwanted higher resistance, then it has influence on all other sensors.
At any time I'll replace this five Tyco spades and see what it gets then.

Regards
Dieter
Dieter K.

Thanks for the advice. I have another run to Dover today and will see if it happens again.I have been thinking about changing the throttle body for a 52mm aluminium one so this might be the excuse I need.
James Forbes Simpson

I do have the same symptoms, throttle body is ok.
On the French side of the BBS someone also suggested a Expansion tank cap issue: when hot, a few drops of steam might confuse the ECU and the engine bay temp sensor.


I'm about to change mine since the rivet decided to migrate from the center. I'll tell you if any changes occurs.


Boris
Boris

I had this issue, but a change to the 52mm metal throtle body cured it.
Steve Ratledge

Definitely worth checking the coolant temp sensor and its contacts. I had intermittent high idle problems over a period of time and changing the sensor (less than £15 and an easy DIY) definitely cured it. Others have found that the sensor was actually OK and that cleaning the contacts cured the problem.
Dave Livingstone

>>
Stage 2.
Changed the Coolant Temperature Sensor.
Investigated and found the old well working and not broken. (Other here found the same, .. Rob?)
<<

Yes, you're right Dieter - I have been down this particular road.

Sensor cleaning covered here: http://www.mgf.ultimatemg.com/hgf_pages/related_problems_overheating.htm - and no, I still haven't corrected the sensor removing instruction: the clip need only be pushed in to remove! LOL
Rob Bell

This thread was discussed between 03/08/2004 and 05/08/2004

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