Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGF Technical - Juddering problem..... update

A few weeks ago the coil got replaced to solve the juddering poblem (after battery, plugs, leads, rotor arm)... Unfortunatly, yesterday we had the same experience as during the Treffen and a bunch of other journeys.

What happens if the car loses it:
- car (1.8 MPi) doesn't pull, starts juddering
- occasional misfire (plop in exhaust)
- waving rev counter when gently pushing the accelerator pedal
- fuel smell behind the car
- stepper motor way out of its position
- power off and power back on solves the problem (for a unknown period).

Car is going in tomorow for some days.

Small note: MG Rover don't have a clue.

Keep you posted.
Erik Baekelant


I have the exact same problem. After the alternator belt broken and changed, the car have the same symptoms that you describe.
The MG dealer thought that the cam belt was old and that the camshaft has "moved" so that the valve opens at the wrong time. He is now changing the cam belts.
I will get the car back on Wednesday and I promise that I will update you how it went. Pl do the same.



Sounds to me like ignition timing is faulty.
Valve timing (eg cambelt) would not be intermittent, it would always be bad, possibly getting worse, never better.
Fuel injection ? I guess it could be over-fueling, but I'd still bet on ignition. They've replaced all the obvious - it's still possible that the replacements are faulty.
I'd look towards the crank sensor - this gives base ignition (and fuel) timing, or the ECU/MEMS unit (the revcounter gets its input from this sensor). The wiring/connectors may also cause problems.
If MGR don't have a clue, then find a competent auto-electrician.

Good Luck !

The false on my car is permanent. The MG dealer has connected a rover service program computer and the only electrician false he got was from the cam shaft sensor. Any tip then? Is it possible that ts the cam belt?


Mark - if the camshaft sensor is faulty then I assume you have a VVC ? If so, then it's possible you have problems with valve timing. Perhaps changing the cam belts (more than one belt also indicates a VVC) will fix the problem - I hope so !
Are you paying for this work, or is it under warranty?

My own VVC had a problem where the engine would not run below about 3000RPM. This was down to the VVC control mechanism.


Erik, after chatting to Kingsley on Sunday, he had a problem that was not too dissimilar to yours (albeit complicated by the fact that he now has a fire-breathing DVA ported monster of an engine!).

Running problem that usually only manefested at higher engine loads was tracked down to be a problem with a failing standard fuel pressure regulator.

The ECU was compensating by pumping more fuel - and making the engine run richer. Result: on over run, you could get detonations from the exhaust as excess fuel was burnt off (could explain the petrol smell you are detecting as well as the poor running).

I doubt that yours will be quite as severe a case as Kingsley's, but the fuel pressure regulator is a very cheap part, is easy to replace, and when faulty could give rise to the sort of problems you've been experiencing with your F.

Something to investigate, I reckon. :o)

If not this, then an electrical gremilin - as the chaps suggest - is the most likely cause.
Rob Bell

Hi again!

Yes the car is a VVC - 96. The problem is also (except that there is no power in the car, i presume that it make 0-60 mph in 17 s) I cant get the engine too run faster than 5000 rpm. Its so strange, it feels like driving a Russian Trabant. Like Erik I smell gasoline and the car misfire. Hope the cam belts fix the problem. Any else tip I can give my MG service man?

>>Any else tip I can give my MG service man?<<

Yes - check the fuel pressure regulator, Mark!
Rob Bell

>>Any else tip I can give my MG service man?<<
From the w/s manual: "If the ECM loses the cam period signal .. the cam period will remain frozen -- Engine speed may be limited as low as 5500RPM." Manual also says a camshaft period fault will only be detected during startup or initial running.
Really, if the fault is not intermittent and is this bad they should be able to fix it.


First of all thanks for the replies....

>>> Running problem that usually only manefested at higher engine loads was tracked down to be a problem with a failing standard fuel pressure regulator. <<<

I don't say it really is caused by a heavier load, but it appears to be more often when hard accelerating and some engine braking is involved. Although this style of driving isn't a guarantee for the problem.

What about the stepper motor being completely out of its position ?

Let's hope they don't change the ECU/MEMS for nothing.
Erik Baekelant

Not sure about the stepper motor calibration, unless there is some kind of compensation for fueling at any speed above idle...

As I say, not necessarily the cause of your problems Erik, but it is something that is cheap and easy to check.
Rob Bell

Can a part of the TB be faulty... I can not remember that I had a problem before the upgrade to TB 52mm.

Just an idea.
Erik Baekelant

update again ;-)

Just had a phone call: it must be the oxygen sensor. On the testbook it reports an error from time to time AND the CO value increases when the revs are increasing, while the CO value must be at the same level all the time.

Hydraulic control solenoid?

>>Hydraulic control solenoid?<<
You mean on Mark's car ? Hopefully, his garage will look here while checking / replacing the cam belts.

The item that got my attention on Erik's car was
>>- waving rev counter when gently pushing the accelerator pedal<<
AFAIK, the revcounter is fed by one sensor only - the crank position sensor. So why would the revcounter 'wave' ?
- the clutch is faulty (bit too obvious!)
- the sensor is faulty/dirty
- the wiring is damaged (so the ECU picks up noise)
- the ECU is faulty - (not likely IMO)

The technician needs to work from first principles, as testbook diagnostics isn't helpful.
- 'scope the HT leads, this is -so- easy on an MPi
- 'scope the oxygen sensor - it has a distinctive output curve if fuelling is OK
- 'scope the crank sensor (pref. at the ECU end)
I think testbook has facilities for all this - but dealer technicians don't use it fully. An auto electrican with a specialised(?) scope can check this in a few minutes.

Get those bl**dy dealers working or take it to a specialist !


I had a problem with the REV counter "waving" after fitting my Trophy Throttle body.

It also seemed to struggle to get up the revs.

Thought it was something to do with fuel delivery.

Got the FSE Power Boost Valve fitted, and also found the Throttle positon sensor was a bit loose.

Anyway, whether it was the fuel valve, or loose sensor, the problem was resolved.

paul weatherill

Well let's hope it was the oxygen sensor.... got the car back after a 642.00 bill.

They changed the exhuast manifold as well, cause the thread where the sensor goes in was totally corroded.
They used a second hand manifold.... if I had knew they wanted to swap the manigfolds, I would have sent one to Mike so they could fit a "new and better" one.

Again a missed opportunity, but let's hope this thread goes into the archives for good.

Mark, I keep my fingers crossed for your car as well.

Thanks guys

knocking on wood !

Dieter K.

Well 642 euro's and 40kms further and the problem is there again.

>>> Get those bl**dy dealers working or take it to a specialist <<<
Is it wrong to expect that the bl**dy dealer is the specialist?

Next thing that will be changed is the fuel pressure regulator, or the dealer need to come will a really good story.

I'm also thinking about the potentiometer on the throttle body. Does that make sense ?

Any partnumbers, how to's or don't-s ?


>knocking on wood !
Sh*t wood.

>Does that make sense ?

No idea, I'm still in the opinion on looking for sensors or broken wires.
Regarding the throttle sensor the revs will increase if anything is wrong with it.

A call to anyone here who upgraded the plastic throttle body to a metal part should help.

Anyone out there who can lean Eric a throttle sensor ???

JZX3419 was the old type number and all who bought a new body have a spare.

Dieter K.

>>> Get those bl**dy dealers working or take it to a specialist <<<
Is it wrong to expect that the bl**dy dealer is the specialist?<<
The dealer should be the specialist - they have the equipment and the training, and given the build quality of the F they should have the experience !

Can you talk to the technician dealing with your car ?
If you have confidence in what he is doing then carry on - even better if you can watch him diagnose the problem.
If you cannot talk to the technician, or have no confidence in their ability then why go there ?
Auto Electricians live by their ability to diagnose and fix problems.


Sorry to hear that news Erik :o(

The fuel pressure regulator would be my next check too - and I'd think about getting a compression test on the cylinders, just to ensure that the gasket is seating properly around the fire rings.
Rob Bell

Thanks for the input guys (again)

Had a phone call with the dealer in the afternoon.
Dealer: Bring the car back in
Me: What will be done?
Dealer: We don't know, have a look at it?
Me: Could it be the Fuel Pressure Regulator
Dealer: In that case the car would stall, so no.
Me: Could it be the potentiometer at the throttle body
Dealer: We allready had a look at the stepper motor
Me: No, I mean the sensor at the throttle body
Dealer: No, stepper motor is OK
. . .
Had a search and found my old plastic TB. Think I will swap it again with the 52mm TB, so if the sensor is tricky the problem would be gone. If that's the case next thing will be swapping the TB's again and the potentiometers.
On the other hand, I will be looking for some info about the Fuel Pressure Regulator... would be nice if I can (at least) locate that one ;o)

Keep you informed

If the fuel pressure regulator is the same as FPV, then the partnumber could be: MKW10016

Guess where I found this one ?

Thanks Dieter !!

*g, your welcome.

Mate you need not change the whole TB.
Only the sensor.
Two bolts with Torx head (can't recall the smal size, may be T15? )

- press connector securing wire bracket and pull off the connector.
- Loosen both screws and keep the aluminum bar.
- pull off the sensor with some force, but DO NOT turn while pulling.
- push on the old and bolt on together with the ally bar.
- do not tighten to much. Low torque.
- reconnect the plug

Reset Stepper as usual (ignition on, 5 times key accelerator, ignition off)
Thats all.

Dieter K.

Erik, check the fuel pump loom connector where it connects to the main loom, this is situated behind the drivers seat(in your car) to the side of the main engine cover. It is a circular plate retained with 4 screws. Remove and check the connections for a poor contact.HTH.

Hi Erik,

this is a mad one - but possible !!

If the 3-terminal connector on the throttle-pot is either forced onto the mating connector on the pot the wrong way around OR the cables have been changed /bad connection/broken the car behaves very funny whenever the throttle is moved. Steady speed can be OK but any change will be like "kangaroo" !
An intermittent fault here will give the same symptoms. Had this problem for a few minutes when I changed to the big Opel throttle body and forgot to change the wiring to the potentiometer :{

BR, Carl.
Carl Blom

Afternoon all,

I have a v similar problem to Erik. Had HGF approx 6 weeks ago and since then have had juddering in 2nd or 3rd gear if the revs aren't quite right. Rev counter needle wobbles too. Acceleration doesn't seem anywhere near as perky as before. Had 5yr service done in Feb so cam belts should have been replaced.

I'm getting checked on Monday - what do you think I should be suggesting they look for in particular?

Cheers in advance

I A Charlton

Ian - where to start?

Have you get an MPi or VVC?

After removing the head to replace the head gasket - and therefore disturbing the cam belt - I'd be initially worried about cam timing: was the correct cam locking tool used I wonder?

But always start with the simple things first, and be methodical. Mind you, given the proximity of the current problem to the HGF repair, I'd be asking the repairing garage to sort the problem out!

One area that causes problems similar to that described are ignition related: if you have an MPi, and it is over 4 years old, suspect the distributer head and rotor arm. On both MPi and VVC, replace the HT leads as a matter of course.

If that lot doesn't work, then move on to the next level of checks...
Rob Bell

Rob, thanks for your thoughts - very helpful as always!

Its an S-Reg VVC and unfortunately the HGF repair was done down in Hereford (near where my folks live) whereas I'm actually in North London and so the work on Monday will be done by Palmsville.

It would be nice to have a least one month of trouble-free driving!

I A Charlton

Just spotted this thread.


Nooooooooo! I thought we had this problem solved on the Treffen (i'm assuming it's the same problem).

For those who are a bit puzzled, it's not just the rev needle wavering, its the engine surging.

It's almost like a resonance wave, basically when it is happening with constant and even pressure on the accelerator the engine gets in to a rythmical pulse say 2000 rpm up to 3000 rpm and back again, like a feedback loop - very, very odd indeed.

What it feels like to me is that the engine is trying to stop, but the MEMS is giving regular surges of fuel to keep it going, amost as if the choke is being opened and closed over and over again on 1 second intervals.

Tried loads of things on the Treffen, inspected the HT leads and the stepper motor amongst others, finally Mike cleaned the stepper motor and all appeared to be well, or so i thought anyway.

Potentiometer is on the back of the TB and is a small, black plastic 'T' shaped item with a white 'half moon' recess in the middle to take the throttle butterfly spindle. Dieter is correct it is secured with a pair of T15 Torx screws, but it is important that they are not overtightened, doing so will make the screw project too far out the back of the potentiometer and this can foul the return spring for the butterfly. Not sure if this could cause the problem Erik, but it certainly sounds to me like an electrical gremlin or two. the other thing to watch out for on the potentiometer is the spring clip that secures the wiring, it has a habbit of popping out when released and is bl**dy difficult to find if it drops into the engine bay! ;-)

Sorry i'm not more helpful mate, but it stumped me on the Treffen and i haven't had any further ideas since. :-(

Scarlet Fever

> it has a habbit of popping out when released ...

That's why it's important to PUSH the spring clip and pull the connector at the same time, not pull off the spring and then the connector ;)
I remember the wrong kind of connector release on Rob's site anywere. Was it the coolant temp site ?
Dieter K.

>>I remember the wrong kind of connector release on Rob's site anywere. Was it the coolant temp site ?<<

Yup, that's right Dieter. I didn't know that then - do now!

Perhaps I ought to correct that "mistake"
Rob Bell

This thread was discussed between 14/04/2003 and 23/04/2003

MG MGF Technical index

This thread is from the archive. The Live MG MGF Technical BBS is active now.