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MG MGF Technical - Fast idle problem (revisited)

1996 VVC, been off the road 2 years.
Fast idle problem, I charged the battery and it started 1st time and revved up to 1500 again with occasional forays up to 2000. A tap on the throttle causes it to drop back to 900 for a few seconds then wanders up again.

Brown ECT sensor checks out ok, as far as the ECU/MEMS plug.
TPS output checked and varies up to around 4.5V with movement.
Occluding the IACV drops the revs, but when revving up to 2-3000 it still appears to be open. Should it not close once a certain engine speed is reached? I thought it was there to provide bypass air when the throttle butterfly valve is closed?
Oh, and the rad. fan remains on.
IACV has been cleaned to no avail.

So- possibilities- stuffed IACV? More major MEMS issues?
VVC sensor???


I guess a testbook session might help but currently located in far North NZ.

All suggestions greatly appreciated/
Charles Dundas

If the rad fan is on, you have no signal for the ECU from the brown temperature sensor; so it will be over fuelling in default mode. You may have a broken sender unit or more likely an open circuit with the wiring. As a cheap starter try 'electrical contact cleaner' aerosol on all of the ECU contacts (it can't do any harm) but definitely on the brown temp sensor contacts.
It is best reached by removing the inspection panel. If the spray doesn't fix it, you can compare the sender's resistance reading against temperature from Dieters site under 'sensors'.
Charless

Checked that one- warm engine and I unplugged the black multiplug at the ECU and got the correct resistance at the plug. Sender ok, wiring as far as ECU ok. Could the ECU be dodgy??
Charles Dundas

Get a T300 - reads OBD1 and 2 ECUs.Comes with the lead you nead to do your own fault reading. Easy as could be!

Cost US$160 including postage.Comes from HK.
I purchased from the below via AliExpress.

HAOSUTONG CO. LIMITED
C/O YFHEX
2RD INDUSTRIAL DISTRICT
HONG KONG,
HK


Save loads of time and fuffing around....
Julian S Foulger

Julian, do you happen to know whether the T300 unit can re-link an engine ECU to an immobiliser ECU?
bandit

Follow link below for more info.

http://www.alibaba.com/showroom/t300-advance-diagnostic.html

I use my reader for reading fault codes and clearing them + getting live data but can be used for reprogramming fobs et al. So in answer to your question Bandit, I believe the answer is yes.
Julian S Foulger

This thread was discussed between 14/03/2012 and 18/03/2012

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