I’m not sure Robbie but it does seem to run slightly better with C4 unplugged. It’s like it picks the revs up. I can comp test the car one evening this week. I’ll also try swapping the coils. I’m pretty sure I put them on randomly after trying the last plug change so I do doubt it’s this.
It turned out to be an O2 sensor and coil? Yea with the tool on it was run with nothing odd looking.
With that car, replacing the coil pack (all four coils), would effect a temporary cure but it didn’t last long and the misfire would return.
Replacing the O2 lambda sensor as well as the coil pack sorted it and kept the engine management warning light away.
Did the Fiesta throw a code? Ive tried fault finding coils by making the car run on 1 cylinder and it runs on them all so I’m inclined to think it’s not coil or spark.
It’s just the fact I have no codes. Still having a mare with it.
Are you absolutely sure it’s a bad idle?? From the video it sounds like a knock…
I think so Chris, it defo misses. Wouldn’t the knock sensor bring up a code if it was knock?
You only get codes when the ECU can’t make adjustments to bring the engine back to pre defined limits or a sensor is dead.
That’s why looking at the fuel trims etc might tell you if the ECU is compensating for something. When mine ran rough and stalled everytime I pulled up to a junction there were no codes. The MAF temp was massively over reading and the ECU was constantly trying to match both the MAF and the O2 sensor. A new MAF made it run like new.
If your car is running rough I’d start at the MAF and the O2 sensor. Look at fuel trims, a positive or minus long term fuel trim over 10% will indicate a mixture issue. Minus is rich and the ECU is under fueling and positive is lean and the ECU is adding fuel to maintain 14.7:1.
The MAF should be around 2.4 g/s at idle for a 1.8 when warm (this is off the top of my head 2L will be higher). If you haven’t got this and a positive long term fuel trim you’re probably looking at a vacuum leak.
If you think your car is missing the ECU can detect this and you’ll have a positive fuel trim and the scan tool should be able to record the detected misfire and tell you what cylinder it is.
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I don’t know… My understanding of a knock sensor is to counteract pre-detonation issues with bad fuel etc… I reckon @DuratecNC would know the answer to that. Similarly, if you ask him nicely he might have a look at your video above and give his expert opinion… 
One thing is for sure, I absolutely wouldn’t start or drive it until I knew for sure what the issue was.
I’ve found a thread where someone with the same issue as me found it to be his EGR valve stuck open so I’m going to investigate this as the weekend. I’ll also invest in a proper tester so can see values etc as at the mo I only have a scanguage.
I’ve got a new primary O2 to go in as well MAF has been ruled out by swapping a new one in.
Hope you get it sorted.
Hey guys,
So many of these people asking for help never resolve it on the thread to help others so I thought Id tell you all what it was.
The EGR was stuck open. What a terrible job it is to get it all off (Took me 6.5h) but the spring was stuck. I lubed it all off and freed it off and have reinstalled and the car is now sweet as a nut again!
Thanks for all your suggestions. and help!
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