Hey, recently got a mk5 fiesta zetec (1.25 petrol duratec engine) and its been driving fine up until a couple of days ago. Car struggles to start, once it does, rpms drop to ~100rpm (yes, 100, not 1k) and has little to no power below 3k rpm. I checked the eml code and it says "Engine coolant temperature sensor 1 circuit range/performance". I checked the sensor and nothing seems visually wrong with it and I don't think it is causing this issue. My guess is the coil pack, but before I pull the trigger on buying a new one, want to see if there's anything else it could be and what to check. Cheers 

Hi Connor, if you are in the UK and you have a 2006 Fiesta then it is a Mk6 not a Mk5

Before just guessing at possible problems, use a Windows laptop with FORScan software (It's free) and a ELM327(modified) connection cable. Then you will be able to check for all Ford specific Diagnostic Trouble Codes (DTC's) which will help guide you to the problem.

FORScan: https://forscan.org/download.html

ELM327(modified) cable: https://tunnelrat-electronics.fwscart.com/USB_Modified_ELM327/p4541936_17045457.aspx

I really don't think this is a coil pack fault.  Usually coil packs are alright when cold, and get worse as they warm up.

Incorrect temperature reading would certainly explain why it's struggling when cold.  Have you tried running the engine with the temp sensor unplugged?

So an update, I started the car this evening, started perfectly fine, no issues, drove it quite hard and no issues. Parked up for 5 minutes, and it had the same issue as before, check engine light is only flagging the temp sensor, but I noticed a lot of steam from the front of the car this time, but I don't see any leaks. I'm gonna order a new temp sensor, if anyone has a link to one that will work on my car (I'm in the UK, so ig I was wrong with the mk too lol) I'd appreciate it. I've looked at the elm reader after writing the first post, I've ordered that, so I'm gonna wait for that to come and see what that flags up. Thanks again, really appreciate it

On 3/28/2023 at 9:02 PM, Connor_Wetton said:

So an update, I started the car this evening, started perfectly fine, no issues, drove it quite hard and no issues. Parked up for 5 minutes, and it had the same issue as before, check engine light is only flagging the temp sensor, but I noticed a lot of steam from the front of the car this time, but I don't see any leaks. I'm gonna order a new temp sensor, if anyone has a link to one that will work on my car (I'm in the UK, so ig I was wrong with the mk too lol) I'd appreciate it. I've looked at the elm reader after writing the first post, I've ordered that, so I'm gonna wait for that to come and see what that flags up. Thanks again, really appreciate it

Got the new reader hooked up, it's showing engine coolant temperature sensor and p2176-E0 electronic throttle control adaptive power strategy error if that's any help. I'm putting a new coolant sensor on it today, but have no clue about the throttle control

8 minutes ago, Connor_Wetton said:

Got the new reader hooked up, it's showing engine coolant temperature sensor and p2176-E0 electronic throttle control adaptive power strategy error if that's any help. I'm putting a new coolant sensor on it today, but have no clue about the throttle control

P2176 basically means the throttle body is knackered.  If the temp sensor doesn't work, replacing the throttle body would be the next step.

They can be bought second hand fairly cheaply, just need to make sure you get the right one for your engine and year.  

Ford Fiesta Mk6 2006 1.25 Zetec 16v JD3 Throttle Body 2S6UFA | eBay