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 - 900 rpm --> xxxx rpm -------...--------> 900 rpm

When I rev the engine (even when not driving, so at 0mph), the engine goes easy to a higher level of rpm (with a lovely sound). OK, no problem.....

Now my question:
When I release my foot of the accelerator pedal, the needle goes down, but very slowly. Is this normal, and if it is, how can I shorten the time to go back to 900rpm.


you have a K&N fitted, have you ?

If possible then refit the old filter box and try the same.. :)

IMO the 'lack' of air resistance causes this behavior a bit.
I realised this 'slow coming back' ofter fitting my 'open' filter.

Lets see what the experts know..
Dieter Koennecke

Oh dear - a clear sign of impending HG failure.

No, only joking. Just jumping on the bandwagon.

This is normal for most engines isn't it? Mine certainly does it too. As long as its not stopping at 5000 revs or anything its normal!

I guess the F just wants to rev and rev!

had this too once, the "piece with the spring" (?) next to airfilter which drives the accelerator cable needs some greasing.
fixed problem for me on the fly.

second time this happened it got worse & worse and final diagnosis was that both VVC solenoids needed replacement. Mpi has only 1 solenoid.

other possibility: stepper engine loosing it... needs simple testbook tuning

perhaps easier for you if I say this in Dutch: het is dat zwart stuk met een veer dat waar een kabel (ā la remkabel fiets) aan vastzit, dat rechtsvooraan naast airfilter zit, dat je met je vinger kunt duwen zodat uwen MGF gas gaat geven zonder aan de pedaal te komen. Wel, door de hitte & stof kan dit stuk wat stroef beginnen werken, waardoor de veer niet genoeg kracht heeft om direct het toerental terug te laten dalen. Dus gewoon met een spuitbus smeermiddel efkes op spuiten, paar keer duwen en gefixed!
Dirk Vael

>easier for you if I say this in Dutch...

>:-) mein Gott, wieviele Sprachen hast Du denn noch drauf ?

Dieter Koennecke

I seem to remember reading somewhere that cars do this to stop the cat getting plasted with unburned petrol....

Stefan Gibney

I'm with Stephen I would have thought it was down to the engine management burning off the fuel rather than sending out through the exhaust via the CAT. But then I'm no expert. :)

Home of the F'ers Gallery and MG Dealer Guide :)
Paul Lathwell

I thought that this was a feature of the engine management software as otherwise the computer would calculate that no fule was needed to return to idle speed once you have let go of the throttle and by the time the computer has reacted to the idle going below 900rpm it would not be able to recover and the engine would stall.

Stepper motor problems used to do early Rover 216's and stalling on reving was a good indication the stepper motor was not synchronised, was not sealing or was not working correctly.

Can you synchronise the stepper motors on and f?

They get out of sync on the 216's with age, as a result of a duff battery or somtimes engine faults which cause constant stalling.

If the stepper motor works ok and is synchronised there could be a problem with an induction air leak or a problem with the taper seat on the stepper motor sealing, this can be cured by extending the stepper motor fully and applyong a small amount of fine valve grinding paste and grinding a new seat for the stepper motor by inserting and rotation the motor. This is only recomended for small scratches where this is known to be the problem. Do not over do it as you could damage the throttle body and stepper motr.

I think that this slow return to tickover is normal though, it is certainly better than the alternative, stalling.

Could be a sticking thottle cable as well.

Incidently on both f'd i've had there has been a mile of slack in the throttle cable. I have adjusted the cable to remove this whilst still giving about 2 mm of play (amount of deflection of exposed cable from centre line without moving the thottle butterfly). I hope to have gained a slight performance gain by being able to open the throttel a little further,I've no ideas if this is true, but there are no side effects.

Generally a sticking throttle cable will cause the engine to either stick at a high rev or faulter (jumpy) on its way down.

The slow 'steady' return to idle is normal.

Octagon Greetings

Can't you reset the stepper by pushing the accelerator to the floor while the engine is off, or am I getting completely confused with something else, it's too early for my brain to start working..... I did this and it cured the problem when it occurred on my F.
Tony Smith

>Oh dear - a clear sign of impending HG failure.
This isn't funny, you scared me to death..... ;-)

No difference between the situation before and after installing the K&N.

This evening I'll go for the lubrication of the cable, that manages the rev-ing. Could it be reached when just undoing the grill-thing in the boot? I don't expect much, but maybe it improves a little.

>perhaps easier for you if I say this in Dutch
And it's perhaps easier for you to explain in Dutch. Anyway, thanks for the intsruction.

But 'till now no further ideas how I can improve this kind of thing ...


>No difference between the situation before and after installing the K&N.

OK, no 'improvement' hints from my side.
Only another instruction to analyse and understand 'how' it works.

>This evening I'll go for the lubrication of the cable, that manages the rev-ing. Could it be reached when just undoing the grill-thing in the boot? I don't expect much, but maybe it improves a little.

Yes, it is. You'll see the cable hose coming from the right side, leading to a bracket, where the cable hose is adjustable fitted. The cable comes out there and leads to the throttle flap segment.

You can check yourself whether the cable stucks.
Let the engine run idle and
A. turn the 'throttle segment' by hand to the left...
B. pull at the cable ...

Everything more is selfexplaining...
Dieter Koennecke

recently only one picture availiable. To show what location we talk about.

Sie the accelerator cable coming from the right.
Below the large area of that red bracket is the throttle segment.

(You'll not find this bracket at your F)
Dieter Koennecke

OK the first check is to establish whether this is a simple throttle cable resistance. Temporarily disconnect the throttle cable and rev the engine by hand. release the throttle and the internal spring will close it. Note whether the engine revs fall differently. I suspect they will and so you have a cable resistance problem.

If the revs settle at the same slow speed then there may be some problem with either the throttle sticking inside the housing or a similar problem with the stepper motor.

Bearing in mind that the breather system does introduce some oil mist that collects and can over a period cause the throttle to stick.

Also some contamination gets into the stepper motor housing at the valve end and it too causes a poor seating of the valve.

Also remember that any leaking air hose such as those that attache to the charcoal cannister or fuel pressure regulator will affect idle speed. The main ECU connection always lets you know in a big way if it become detached or leaks!!

Try this and see what you find.

Roger Parker

I had this problem with my K-Series engine and lived with it for ages - revs would 'stick' for 2 or three seconds if I let the throttle off below 4500rpm
I spoke to a man from Rover who said "Stepper Motor". We let the engine tickover at the desired rpm then just unplugged the stepper motor and problem solved - revs drop instantly. I havn't bothered to plug it back in since (3000 miles ago).
I not sure I should advise you to do this - I don't know what the effects/damage it might cause on the engine/cat etc but you may choose to try it briefly as a test.

Russell Morgan

Does the f have a throttle switch?

I have no idea on the f so ask the question of those who know, but on Rover 214's there is a switch on the accelerator pedal which tells the engine management when there is no presseure on the accelerator and the engine management goes into idle mode.

If you try to move the throttle cable at the engine end the engine missfires and behaves very odly as it tries to maintain idle speed st full throttle.

Thinking about this the 214's I've played with were all single point injection so I could be typing drivel (no change there) (better get in there first before the rest of you do).

Antway,just a thought.

Hey guys,

I have been reading this BBS for a while and picking up on some of the problems that seem familiar to me.
So is this reving problem.
When shifting dow gears (3->2->stand still), my revs sometimes get stuck @ 3000rpm. Hitting the accelerator pedal once usually make the revs go down to 850rpm. Donīt know what it is, dealer will look into it next Wednesday. And yes, my fuel sender unit needs to be replace too (ran outta fuel on E40), and yes, my speedometer needle wiggles +-2km/h, and yes I hear squeeking noises and yes, my aricon unit leaked inside the passenger foot(floor)well, and yes, my air vent distribution in the car doensīt work anymore (turning the knob to windscreen, passenger or footwells, doesnīt make a difference at all, air keeps coming out everywhere, even when I close the vents manually haha)... I donīt wanna hear it no more, my car only has 9450km on the clock. And I am still not getting nervous,

An optimistic Fīer, David
RKL 856

Optimistic Fīer, David

So you still think that the car is great too??

Stefan Gibney


The car has a very nice driveability. Curved roads are itīs (my) preferred terrain. I like the gear shifting (w/o quick shift), it has a great line. The finishing (even exterior)is a bit crappy (compared to Alfa Romeo Spider i.e.). But you can change a lot, using after market products. At the moment my car is at the dealerīs, ..., again. If Iīd paid 1000Ģ more, a BMW was mine, but as my dad drived a *B* in his younger days, I became victim of nostalgia. I think there is no excuse for Rover/BMW for having that many defects, this soon. To be honnest, I donīt think mx-5īers suffer that much. Anyway, would not wanna drive a Jap though.

David FAO Stefan

This thread was discussed between 21/10/1999 and 28/10/1999

MG MGF Technical index

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