MK4 Fiesta, misfire? Help.

[MK4 Slowride]

My car loses power sometimes, doesn't stall just jitters. It's solved by depressing the clutch and giving it a bit more power.

It only seemes to happen first thing in the morning from cold waiting at the lights that are on quite a steep hill going up. The cars got plenty of fuel and it's not happened anywhere else?

I'm thinking it could be the MAS flow sensor or a misfire (dodgy spark plug?)

Any ideas?

[M-Ster]

sounds like automatic choke or idle control valve would be more inclined to think it was the first as it only happens in the morning my cousin had this on his mk4 i would recommend pick up one from a breakers try that if it works buy a new one or just use the second hand one if it doesnt work at least you will have only lost about a fiver.

Another thing you could try is letting the car warm up for 10 mins before driving it then try driving it up the hill see if the same thing happens if it doesnt i would be 99% sure its auto choke

lt me know how you get on

[MK4 Slowride]

Cheers, is it easy to change the auto choke around then? Sounds quite specialized & I'm an amateur when it comes to engines.

[M-Ster]

think you will find it fairly easy just read the work shop manual if you have one think its a simple unbolt and bolt on just not sure where abouts on the inlet it is

[Geoff82]

Could be either the idle air control valve or the MAF. Before you go replacing perfectly servicable parts, I'd give both a clean with some carburettor cleaning fluid. A lot of the time these sorts of problems are caused by carbon build ups - especially on higher milage engines.

Is this a problem which occurs when stationary or when driving? Idle air control valve problems tend to surface at idle, funnily enough. MAF sensor problems tend to rear their ugly head under heavier load conditions at first.

Edited by Geoff82 on Tuesday 16th December 20:29