Evening all 
I've been having intermittent problems with spluttering/misfiring in my 2003 2.5i (auto). When it first occurred I had just filled the tank, so my first thought was iffy fuel from the supermarket however I ran down the tank, filled up with V-Max and the problem happened again. It got to the point where the car was misfiring on idle, EML, limp mode etc. and finally stalled on the side of the road - which for an automatic is quite an achievement!
Having read up here on the forum I figured it must be a dodgy coil, so desperate to get the car back on the road asap I replaced all six coils and all six spark plugs too. All was well, the car was fine immediately after replacing them (about a month ago).
Now however it has started playing up again and I think I've pinned it down to when I brake (hardish). If I slow down nice and gently and come to a stop at some lights etc. then the car behaves. However if I have to brake with reasonable pressure, nothing major!, then the revs dip to around 400rpm and the car starts spluttering and bounces up and down between 400-600rpm. Obviously being an auto there's little I can do other than come off the brake and move gently forward or put it into neutral and gently blip the throttle. Both of these settle the revs and it sits idling quite nicely again.
Because it's still quite intermittent it's been difficult to pinpoint the exact cause, but pretty much without fail I can make it happen if I brake hard.
A couple of other things that may or may not be relevant. I don't think my battery is in great condition - all electrics work fine and I've never had a problem starting the car, however I can't lock my car with the alarm as without fail sometime during the night the alarm will start chirping. I just lock the car with the key nowadays therefore bypassing the alarm, however I have read that the alarm problem can be caused by an iffy battery hence why I think the battery might not be 100%. I've tried disconnecting the bonnet sensor and it still does it, so ruled the obvious problem out.
Another might be the weather. I don't remember this happening at all a few weeks ago when the weather was nice. However when it first happened we had some really wet weather, and again recently it's been raining hard most days. Possible coincidence but then again perhaps not?
If driving the car in sports mode it's very rare for it to start spluttering.
90% of the time it doesn't throw the EML up - only if I don't nurse it back to life straight away by blipping the throttle, moving off etc. If the EML does come up I usually pull over, ignition off for 30secs, then it starts back up first time and is as right as rain again.
Anyone got any ideas?!
I've been having intermittent problems with spluttering/misfiring in my 2003 2.5i (auto). When it first occurred I had just filled the tank, so my first thought was iffy fuel from the supermarket however I ran down the tank, filled up with V-Max and the problem happened again. It got to the point where the car was misfiring on idle, EML, limp mode etc. and finally stalled on the side of the road - which for an automatic is quite an achievement!
Having read up here on the forum I figured it must be a dodgy coil, so desperate to get the car back on the road asap I replaced all six coils and all six spark plugs too. All was well, the car was fine immediately after replacing them (about a month ago).
Now however it has started playing up again and I think I've pinned it down to when I brake (hardish). If I slow down nice and gently and come to a stop at some lights etc. then the car behaves. However if I have to brake with reasonable pressure, nothing major!, then the revs dip to around 400rpm and the car starts spluttering and bounces up and down between 400-600rpm. Obviously being an auto there's little I can do other than come off the brake and move gently forward or put it into neutral and gently blip the throttle. Both of these settle the revs and it sits idling quite nicely again.
Because it's still quite intermittent it's been difficult to pinpoint the exact cause, but pretty much without fail I can make it happen if I brake hard.
A couple of other things that may or may not be relevant. I don't think my battery is in great condition - all electrics work fine and I've never had a problem starting the car, however I can't lock my car with the alarm as without fail sometime during the night the alarm will start chirping. I just lock the car with the key nowadays therefore bypassing the alarm, however I have read that the alarm problem can be caused by an iffy battery hence why I think the battery might not be 100%. I've tried disconnecting the bonnet sensor and it still does it, so ruled the obvious problem out.
Another might be the weather. I don't remember this happening at all a few weeks ago when the weather was nice. However when it first happened we had some really wet weather, and again recently it's been raining hard most days. Possible coincidence but then again perhaps not?
If driving the car in sports mode it's very rare for it to start spluttering.
90% of the time it doesn't throw the EML up - only if I don't nurse it back to life straight away by blipping the throttle, moving off etc. If the EML does come up I usually pull over, ignition off for 30secs, then it starts back up first time and is as right as rain again.
Anyone got any ideas?!
1066 Country
I didn't even know brake boosters/servos existed so I learnt something new. I guess this was somehow leaking after braking and would obviously then upset the amount of air entering the manifold like you said.