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MG MGF Technical - Fast Engine Idle Speed - I'm At A Loss

Hi everyone i wonder if anyone can help me with the problem below.

Basically i own a 1999 MGF VVC which i have been having some probems with.

My problem started when very occasionally my engine idle speed would go up to approx 2000 revs when my car was stationary and my engine was warm. This didn't happen all of the time but i took it to my local MG dealer to look at.

They informed my that my throttle body was sticking and replaced it with a new one. Basically since leaving the garage afer this work was carried out my car now idles at between 1500 and 2000 revs when warm and is basically worse now then before the done the work.

I took my car back to my dealer to solve this problem and they have had my car now for the last week and still do not know what the problem is.

They have checked the vvc hub,which was fine, checked for air leaks but there were none. They have tried replacing the oil and coolant sensors, still the engine continues to rev at this high speed. They even tried fitting another ECU from another MGF to see if that was the problem but still the idle is two high.

I suggested to the dealer that it may be a throttle cable problem but they say that this problem still exists with the throttle cable disconnected.

They now tell me that they are going to need more time to diagnose this problem as they are at a loss.

Does anyone have any suggestions as to what this problem may be as i am at a loss and my dealer doesn't seem to have a clue. It seems to have got worse since they changed the throttle body.

Im sorry this thread is so long i'm just after some sound advise.
C Barnett

I think it could be the wiring harness between sensors or the IACV and the ECU.
No sense of other VVC speciallities from my side though.

Had similar troubles with my MPi and was able putting it down myself to a contact problem with the black connector to the MEMES ECU. *Found by coincidence*
A dealer visit and Testbook session showed no failure. Idle mode drove me nuts over month and we discussed with loads of hints from friends here at the BBS. A search in the archives for *idle high* will bring up several threads.

The nearly all ended up with 'touching' sensors and replacement, changing harness etc. I fear most could have been put down to bad connections only. Cured by changing the part but basically may be the connector re-routing or 'cleaning connectors' was the true problem ?

In my problems case the cable inlet of the connector had to much force put on due to a missing cable tie at the ECU bracket.
http://www.mgfcar.de/mems1.9/harness_loose_sc02513.jpg
Over month the sensor contacts had been bent downwards. A simple re-routing of the harness in smooth bend and taking away any force to the connector has cured the troubles. Or better said, I had no high idle since I re-routed the harness at that location and pushed in the missing cable showed in the above pic.

There've been more with similar problems (Erik, Tom and some more)

HTH
Dieter
Dieter K.

Sounds like a sticky Idle Air Controller to me, the same symptoms I was experiencing. While the engine is warm and idling fast, squeeze shut the hose leading to the intake manifold. If idle speed drops it is a good indication this is the problem. The coil packs in the IACV can be rebuilt by a competent technician, you can install a gate valve or restrictor in the air tube, or replace the valve (quite expensive). Good luck.
Grant

Had a similar problem after I fitted at Trophy throttle body. The idle speed is related to (controlled by ?) the throttle position sensor (TPS) and needs to be set using Rover Testbook. When I changed the throttle the idle speed was 2000 RPM on my MGF. I fixed it without a visit to the Rover dealer by swapping the TPS from the old throttle body with the new one. The idle speed went back to normal. I am surprised the dealer was not able to sort it.
Paul Robertson

I had a similar problem after car had been at a repair shop for about 6 weeks. Car came back with a flat battery that never really recovered - started the car but always sounded like it was struggling. I thought that the two couldn't be connected but after changing the battery the problem went away.

Just another possibility to look at.
John Pickup

Paul,

I hope you didn't pay for the dealers useless Testbook works.
_This_ adaption of the TPS can be done without Testbook by anyone at any time.

- Ignition on. (don't start the engine)
- key the accelerator five times within 10 seconds.
- Ignition out

Start engine.
TPS adaption done.

Rgds
Dieter
Dieter K.

Nothiing to add, except summarise:

1. TPS (Throttle position sensor) - sensor itself can be faulty, as can a connection or even a wire break in the loom.
2. IACV (Idle air control valve) - common source of unusual idle speeds. May require replacing, in which case second hand from an autobreaker such as the MGF Centre is likely to be the cheapest route.
3. Leaking inlet manifold - gasket failure, or a throttle body that hasn't been seated properly to the plenum. Hopefully your dealer has checked all this already
4. Loose wire to the ECU - I recall all the "fun and games" that Dieter had to go through before coming to the bottom of this perplexing problem!!!
5. Sticking butterfly throttle valve - often down to grime clogging things up, but may also be caused by a warped throttle housing: http://www.mgf.ultimatemg.com/Throttle_body/index.htm#problem

Good luck - hopefully the problem will be solved soon!
Rob Bell

This thread was discussed between 21/02/2004 and 23/02/2004

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