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MG MGF Technical - Follow up: juddering, jumping revs

Some will still remember the juddering/performance/misfire problem and dropping revs of my F during the Treffen. Since then, the problm happened now and then, mostly during "garage-closed-hours".

Last Thursday we got the time to put the F on the road, do some test driving and end up with the faulty F at the garage.

During the problem the testbook gave the following errors:
- Stepper motor position too high (and it was way too high), but was set correctly after powering off and on again.
- ECM Inlet manifold vacuum pipe condition: pipes got been checked, but they are OK. By MG Rover, this could not cause the problem and I don't need to worry about this one.

Suggestion of MG Rover: Try replacing the coils, it's a guess, but we need to do something.

The car will be in next week, on Tuesday.

Oh and euh.. the technician was a bit worried by the K&N... could this 'cause some malfunctions. Hahahaha, I guess he didn't notice the Trophy TB, the missing cat and the 3rd party exhaust ;-)

Erik, I guess you've checked and changed the plugs and HT leads already?
Rob Bell


About three times on last years Treffen - courtesy of Mike Satur:-)

Ted Newman

Well, given the group on the Treffen, that comes as no surprise Ted! LOL

Perhaps a next step will be to replace the MEMS with another unit to see whether there is a problem with the engine management system.
Rob Bell

>>>ECM Inlet manifold vacuum pipe condition<<<

A very potentially telling fault!!! Since the very fact that Testbook highlighted this points to the fact that it detected a manifold depression reading that was out of range. Normally a good fully warm engine will be giving between 30 and 40kPa reading when idling and higher readigns according to throttle postion and load. What was the idle kPa reading?

If it was outside the above range then this will have a quite pronounced effect on the engine operation and any leaks through bad connection or broken pipes etc will see a much higher figure and lead to hesitation and misfire. The fact that the fault gives an intermittent showing may indicate that the problem varies in degree and so could well be a candidate for one possible cause. Double check the vac pipe from manifold to ECU and suck on the pipe into the ECU and wobble the pipe about. This may help to show if a leak is present.

Roger Parker


Have you tried a new battery??

Stefan Gibney

I remember leads got changed and distributor, but not the coils.
Dieter K.

Sorry Erik, no warranty claims please;-)

Yeah Stefan, I remember your advice about changing the battery, but the new one didn't solve the problem.

Rob, The leads, plugs, rotor and distributorcap got changed by and with the help of all the Treffeners. I was thinking about the MEMS myself, and mentioned that at the garage, but they wanted to change the coils first.

Roger, I've got no value, as the 'Inlet Manifold vacuum pipe' thing only showed up at the global diagnostic. Something you could start at the testbook and the result is a list with all the succesfull's and failing tests. The technician said he could hardly belief there's something wrong with one of the inlet valves because the problem of the bad running engine stops when the ignition is switched off and back on again. Next time the car goes in with the problem, I'll let them check the value and pipes again.

Thanks for your imput guys, I'll keep you posted.


Hi Erik, yup, we're on similar wavelengths here. I guess it would be easier to look into other causes of poor running if a 'spare' ECU and imobiliser weren't readily to hand.

>>The technician said he could hardly belief there's something wrong with one of the inlet valves because the problem of the bad running engine stops when the ignition is switched off and back on again.<<

Might also be worth checking the inlet manifold gaskets. A vacuum leak can occur almost anywhere!
Rob Bell

This thread was discussed between 24/02/2003 and 25/02/2003

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