2007 Fiesta MK6 1.25

Morning. So, for a few weeks now. I have experience an odd acceleration issue. What seems to happen is, I will change gear (can also be any gear) and I experience what I can only describe as lag? It’s not a consistent thing and it doesn’t happen every drive. So upon changing gear, I can put my foot back on the accelerator but it will not rev/move for at least 1/1.5 seconds, and then it will rev/move. There was also a journey where I was doing about 55/60 and the car juddered like it was losing power, another time where I was idle and the car almost stalled. I should also add that I changed the fuel filter and for about 2 weeks I didn’t have this issue but yesterday it came back

So far I have;

Done a service (air/fuel/oil filters, sparks & oil)

Changed HT leads

Changed Coil pack

I have also changed the 02 sensor about 3/4 months ago due to a fault code that came up after a dash light emerged. 

I’m prepared to buy injectors next but of course I don’t wanna be spending over on a car that’s not worth all too much these days, also don’t particularly want to take it to a garage. 
 

I have thought “clutch?” But surely if it was a clutch issue I would have issues changing gear etc. it feels like an acceleration issue. As I said, I can only describe it as lag, it’s like the car is waiting for it to be fed something before it will make its decision. Not particularly great when it does it on roundabouts ha! 

 

TPS sounds most likely.

Clutch slip results in no more speed, but revs shooting up, so it doesn't sound like that.

If the new 02 sensor was a cheap aftermarket part, I wouldn't rule that out.

@TomsFocus didn’t think of TPS but again wouldn’t that occur more often? I don’t get it every journey and it sometimes feels like once the car has warmed up that it doesn’t do it anymore either. Baffling stuff. I am also going to get a better 02 Sensor now because I remember buying a cheap one at the time.

I just took the car out on a cold engine again, wasn’t doing it for the first mile, engine still cold at this point, turned the air con on and it was doing it once again, juddered really bad this time and ended up going down to 300 revs at a junction before going back up. Once the engine was warm, no issues with air con on hot or cold. Bizarre.

Best option would be to get Forscan in that case.  That'll show you any hidden fault codes.  If there are no codes you can watch the live data streams to work out which sensor or actuator is failing.

I really don't think it's the injectors myself.

@TomsFocus neither do I but wanted to clear all avenues as much as I could before garaging it. I’ve bought a new branded 02 sensor in any case but will go about getting a forscan if it continues.

 

Thanks for taking the time!

I don't know if your model has a MAF sensor but I had a similar problem with a Nissan Primera and that turned out to be the MAF sensor. Don't go for a cheap Ebay one as they don't work properly get an oem one.