just got home from Mountune, got them to check this out for me as i wasnt sure if it was possibly connected to the upgrade.

My symptoms were exactly the same as those Cherie listed at the start.

Altho the guys in the garage cant say 100% what it was, theyve taken an educated guess at it.

What they believe it is is the 'front hego sensor' in the exhaust. They think that that was faulty and wasnt operating correctly with the back sensor so it wasnt idling correctly.

What theyve done is installed a new one on the car, if it works fine and the problem doesnt return then everything is sorted. if it does carry on doing it then i need to take it back and theyll put my original back on and carry on trying diagnose it.

So keep your eyes posted on here for updates from myself!

i did mention to them that other people on here were having the same problem with different setups i.e. standard, custom mod route etc so theyve asked me to let them know what everyone elses outcomes are as theyd like to know about it if it is a common problem. so maybe well see a Mountune hego sensor on the site soon

Must say, the blokes there are fantastic, absolutely first class service from them again today

Sounds good mate, thanks for the post, let us know if it sorts it.

I've got something slightly simpler to try tomorrow: a new air filter. Although she had a service in April, it was only a minor one and it wasn't changed. Thought I'd check it, and it's filthy even if it's not the cause, it needs doing.

If it doesn't cure, I'll try the ECU reset tomorrow instead.

Hows the car running?

Mines still doing this, revved it upto 2krpm tonser if it would clear, but you can feel it not getting the air:fuel right, only does it for a minute or so :/ will have tonrset the ecu tomorrow!

Decided this morning to disconnect the battery and leave it so over night, at the same time ive cleaned out my k@n57i and left it to dry, i got a video from the exhaust basically showing what i hear an can see by judging the revs but will put it up later.

Oiled up the k&n this morning and re-installed it. Reconnected the battery and all is well, sat here with the car at idle and now no problems at all, happily sat there at around 11krpm and dropping bit by bit until it heats up. Revved it a bit and revs went straight up instead of dropping first. Going to take it out for a quick raz now!

Called the special Ford Hotline again.

THey told me every ST and 1.6 Liter fiesta has this problem.
it's 'normal'.

So every ST is meant to have the revs drop that low on choke that it stalls? Sorry, but that just sounds like the typical Ford bollocks for 'we don't really know and we don't really care'.

Someone on STOC has fixed this problem with a new battery. I believe Stason may be trying it too. Be great if it works, simple fix.

yep definitely feasible to cause it, over time the battery cells start to deteriorate, usually not so soon.

not sure what the science is behind it but im guessing dead battery cells generally mean the other functional ones are put under stress been used and charged at the same time.

it's like trying to get 5 people in, and 5 people out of one door at the same time.

Yeah, starting the engine is definitely going to put strain on a battery not operating at full power. If it works for you and the other couple of people trying it I shall be buying one on payday too.

i apprechiate what STASON's thoughts are on it, but as soon as the engine turns over the alternator produces more then enough current to support the entire car