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MG MGF Technical - it was a nightmare, real kangaroo stuff !

Towards the end of a long run recently I have a strange misfiring issue. I had driven nearly 200 miles so the engine was good and warm. Going in to a tight bend I changed down rather enthusiastically in order to keep the revs high. Then as I went round the bend keeping the revs steady it started to get jerky. Then if I accelerated hard it was normal however if I was gentle with the accelerator is was very jerky.

When I held her at 2000-3000 revs it was a nightmare real kangaroo stuff and reverse parking at low revs was a real pain.
When parked I noticed that the revs at idle went from 800-1000 rpm in a rhythmical manner
I stopped the engine and restarted it. It started with no fuss but the jerkiness was still there.

Cold starting - no problems
Next day the issue was gone. I have since done about 1000 miles with no hint of a problem.
I have had same symptoms before (but much milder) and normally a restart cured it. In fact I replaced the rotor arm and dizzy cap about a year ago after the last occurrence.

So what now
Step 1 - I will change the leads for 8 mm High Performance magnecor ones this weekend but what else should I do?

A search of the archive points to the idle air control valve or various temp sensors.

How do I identify these various sensors and then what a clean with electrical contact clearer?

Suggestions gratefully received.

Hoping to have new cams fitted in the next week or two. So I need to get rid of this problem in case it clouds any future issues!
Steve Ratledge

Has it been wet each time this has happened?
Pete Turnbull

When I bought my MGF a couple of weeks ago i had VERY similar troubles. It would start atraight away and tick over well until it "coughed" and then would slowly jerk itself to a stall. Mid revs (2000-3000) it would die too!
Have a look here...

check under technical (top right selection box of 4) and near the bottom is a bit about failing rotor arm and distributer cap.

Thought that would solve it till i got the engine bay cover off and found I was 200 cars into the wasted spark/ non-dis. cap model!!

Then MG Rover themselves looked at it and found the EMS light was coming on and that a "few" engine management sensors had failed. They replaced them and now she runs fine. You could always try that?

Good luck.
S J Knight

I've already replaced the rotor arm and distributer cap. Its details of the sensors that I am after.

Pete no, not related to the weather at all!
Steve Ratledge

hmm, yes there i was a bit of a mug. As it was done under warranty and i was glad it wasn't the dreaded U-Kno-Wat... I didn't ask. They said that putting it on the diagnostic machine showed that it had a few error messages and they weren't sure which one was related. They wiped the memory and told me to drive it until the EMS light came on. It did in about 4 hours and so she went back in.
I'll pop into the garage tomorrow and ask a few questions.
S J Knight

>tight bend I changed down rather enthusiastically in order to keep the revs high.

my MGF (mpi) suffers from a similar problem, ... sometimes. I think it is the same.

I put it down currently to anything running mad with the vacuum sensure inside the ECU. Have investigated each and everything in the last years with no final solution.

Occurance at mine, and I can re-produce easy:
When going downhill in low gear with _engine brake_ (spelling?). Means, the engine runs in high revs near 4000..5000 or like that and no fuel from the accelerator.

From technical view there may some facts have influence.
[please, someone may correct any wrong ideas]
- no fuel to the engine, but high cold airflow
- catalyst gets cold ?
- oxygen sensor may play up ?
and steady high vacuum to the inlet manifold and the mentioned pressure sensor.

Don't laugh, but:
It happens every year on our Alps trip to South Tyrol up in Austria. Motorway down to Zirl near Innsbruck.

After about 2 to 3 minutes downhill in high revs. When going straight and accelerate it jumps and judders like a kangaroo.

Nothing helps, but stop and shut down the engine. Wait for 5 to 10 minutes. Start again and it's solved.
Did each and everything like resetting the throttle body sensor, rattle at the ECU connector etc.

I've sourced a second hand ECU recently and will see what it does after a change.

Apology, forgot the link to the sensor document

Check the ECU connector and thin Sensor wires going in there immidiately aswell.

Thanks Dieter. I shall try and recreate what you have discribed and see if I can get it to happen. But what you say sounds very familar. (Mine is a 1998 mpi).
Steve Ratledge

I had a similar problem, removed the plug from the water temp sensor on the inlet manifold cleaned and replaced been running smooth as a baby's proverbial ever since. About 4 months.

If it helps ive been having similar issues with my vvc since the wet weather started.... It was jumping around when pulling way in low gears, and stalling far to easily!

One set of Magencor 8.5mm Competition leads later (the 8mm are perfectly adequate!) and my problems dissapeared! Much smoother throttle, and I can pull away without having to appply any accelerator pedal which I had to before! On inspection I discovered I was still running the original OEM leads from 7 years ago, so not bad considering!

I had an issue when I first got my car. Exactly the same symptoms. Turned out to be a dodgy throttle position sensor.
Alex T

Steve, the "other" sensor that can cause bad idling and running problems is the crank position sensor. Neil and a number of others have reported this problem - and the reports are in the archives.

A check with Testbook ought to yield the relevant reports on the condition of the sensors.

Good luck!
Rob Bell

Nkosi said <<I had a similar problem, removed the plug from the water temp sensor on the inlet manifold cleaned and replaced been running smooth as a baby's proverbial ever since. About 4 months. >>

I think the sensor on the inlet manifold is air temp not water.

Bruce Caldwell

Well there you have i guys... I'm glad that i can finally be part of the norm.
The MG mechanics said they replaced the Inlet Manifold and Crank (Piston) Sensor. Actually I'm told the CPSensor was "failing" so they replaced it anyway.
So I assume both sensors down together was why the poor girl couldn't get her act together. It's a wonder she started at all.
S J Knight

This thread was discussed between 02/12/2005 and 03/12/2005

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