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MG MGF Technical - revved right up

I've noticed something a bit strange whilst driving around - especially when in the traffic on the journey to work, as I barely get out of 2nd gear grrrrrrrrr :-(

When I'm in 2nd gear & I need to brake to stop, as soon as I start braking then depress the clutch, the revs shoot up momentarily, to between 1200-1400rpm (only for a second) then go back down as soon as I stop.

Its more of an irritation than anything else....does anybody have any ideas what the problem may be? I hope its not too serious.

Thanks
Fiona :-)8-<

'97 VVC
Fiona

Fiona WROTE:

>>depress the clutch, the revs shoot up momentarily<<

Purely shots in the dark here Fiona.

Do you wear wide clumpy frumpy shoes like some modern females like to do? Glad to say elegance is coming back into women's shoes lately....If you do you may just be catching the throttle pedal as you lift off the throttle pedal (accelerator) onto the brake.

Another possibility, there could be some piece of junk fallen down around the pedals so that when depressing one, it also acts on another pedal nearby.

Then there are many other possibilites such as sticking (slow to return throttle cable) or throttle return spring..... could be anything really.

Anyone with some MGF 'nouse' living in Avon area who could give Fiona's F a quick onceover?
John McFeely

>>Do you wear wide clumpy frumpy shoes like some modern females like to do?>>

No I don't John, I've worn about 5 different types of shoes whilst driving, even trainers - always the same problem. Even get the prob whence driving in my 4inch heeled black leather knee-highed boots ;-O

I wonder after mentioning the above I might get a flurry of offers to give me the 'quick onceover'....LOL

Thanks for the suggestions though, if anybody else has any ideas I'd be grateful. I'll have them check it at the garage when it goes in for the service.

I dont know about junk down amongst the pedals, but today I managed to drop my jetwash token down into the gearbox...i put the token just under the gearstick while I was waiting and it slipped thru a tiny gap and fell down. Can't get it out. Had to buy another one grrrrrrrrr. "Is it cos I is blonde"

Fiona ;-D
Fiona

Hi Fiona - no the engine speed shouldn't go up like that on depressing the brake pedal. Like John, I'd suspect something innocent first, but if you're satisfied that this isn't the case, then it is time to look for another cause.

How firm are your brakes? Coolant levels okay? Does the engine speed fluctuate under other circumstances? I wonder if there isn't a vacuum leak somewhere in the manifold....
Rob Bell

Do you have mats in the footwell.

I had a strange sensation everytime time I pressed the clutch and release could feel the pedals move. This was found to be the mats creeping up behind the pedals and everytime I pressed the clutch the mat got hooked up.

Maybe something similar.

Tom
tom randell@ work

If I understand correctly, then I think the answer is that there's nothing wrong. Happens to me too.

If you brake in 2nd, for example, such that your speed drops to a crawl and the engine speed reaches around idle then MEMS adjusts the fueling of the engine to maintain the idle speed. When you drop the clutch, you suddenly release the load the engine was subjected to and since MEMS has adjusted the running conditions the engine speed rises. It then falls back to normal as MEMS adjusts again. This is most noticeable on slight upward hills - if you stay in 1st and take your foot off the throttle the car won't stall - it'll keep going at engine idle speed. Drop the clutch and you see the revs rise then fall.

At least, I think that's what's happening! :)

Tim.
Tim Jenner


My guess is the throttle position sensor... or wiring.

...assuming it's not the normal anti-stall thang coming in as Tim suggests.

Fiona, if you blip the throttle do the revs drop straight away to idle? If they take an age to go down then it may be this sensor thang as happened to me.

P.
Paul Nothard

Tims quite right, there are two mechanisms here, one is called 'soft landing' and the other is as Tim discribed. The engine management attempts to keep the revs up, it does this by opening the IAVC (throttle bypass valve) and add petrol, so even if you think the car is 'idling' the engine managemnt unit is stuffing in petrol and air at the rate you would have to if you were driving an older car. So when you unload the engine the revs pop up untill it gets a handle on the mixture. The other is when you unload the engine from open throttle, at open throttle the MEMS (engine management) opens the IACV as well, so when you let the throttle go air continues to be passed into the engine to sweep thru the petrol that has been injected (about 1200rpm), only when this mixture is stable (a second or two) does the revs drop back down to idle (900 ish)
Will Munns

<< How firm are your brakes? Coolant levels okay? Does the engine speed fluctuate under other circumstances? I wonder if there isn't a vacuum leak somewhere in the manifold....>

Brakes seem firm enough, checked coolant yesterday - up to the level, but must say looked a bit brownish from what I can see (no....please....no...not the dreaded) and engine speed seems fine at other times.


<< Do you have mats in the footwell >>

Yes and its not that as I checked

<< Fiona, if you blip the throttle do the revs drop straight away to idle? If they take an age to go down then it may be this sensor thang as happened to me >>

The revs seem to go straight down. Although aways when I start the engine from cold its usually running about 1000-1200rpm for a short period until it drops down to 800rpm.



Sounds like its the MEMS jobbie then, in which case I shan't worry too much about it.

Thanks to all
Fiona :@)


Fiona

This thread was discussed between 25/01/2004 and 26/01/2004

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