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MG MGF Technical - Fluctuating revs and loss of power when warm

I've got a 99 MGF, and recently it's decided it wants to start coughing. Initially it would loose power when being pushed very briefly and then recover.

In an effort to remove this gremlin, I have replce the dizzy cap and roter arm, plugs and HT leads.

The problem has developed into a more, erm, interesting one since:

When I push the car fairly hard (although only for maybe two or three minutes) along the ring road back from work (ie, the car's warmed up beforehand and I put my foot down) it'll decide shortly afterwards that it wants to have a mind of its own, and will start to indicate revs of 2000-3000, which will fluctuate as it attempts to idle no matter what the throttle position. If left to idle, the revs will fall, and nearly stall before the ECU catches it. If the throttle is opened and the clutch brought up, there is no power, and the car will try to stall.

If you try to start the car after this stall it won't - it needs a few minutes rest to recover and then will start, although it won't be it's usual self. Left to cool overnight, it's fine again.

Having had it stall on me twice and then not start on busy roads, I need to fix it!

My thinking is that it may be fuel system (filter, pump) related? Pump overheating and then not recovering until cooled?

I'd be grateful for any suggestions.
A Hulse

I would suspect the idle air control valve (IACV) first - it could simply be dirty (remove and clean - worth a go) or it is simply at fault.

Might also be a leaking inlet manifold?
Rob Bell

Put it on testbook and read the fault codes. I had a faulty map sensor and it was the only way to find it.
Stuart Elliot

Well, the car successfully got to the MGF Center and is staying there for a few days - Testbook couldn't complete due to the battery being very undercharged after it's adventures of the last few days!

Hopefully I'll find out more in the next few days.
A Hulse

Is it a VVC ?

I shoudl have mentioned: not, it's not a VVC, it's the standard MPi
A Hulse

It would'nt suprise me if your fuel pump is faulty i had the same with a 97 thought a cangaroo was in the tank you could hear the pump as soon as the key was tuned then quietness and no zoooooooom no fuel or pump ouch got one from a TF for 25.00.


I've got the car back! Hurray!

It turns out the throttle body sensor had failed, making it read 65 on testbook - the maximum it should read is 25! This meant the engine was being fed too much fuel and flooding - hence why it would die after working hard.

A nice new alloy throttle body should hopefully result in no more problems.

*Crosses fingers* This should be the end of it, but i hate it when a thread ends without an answer, so i thought I'd finish the story!
A Hulse

This thread was discussed between 06/01/2006 and 11/01/2006

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