Adding this for anyone that comes across the same issue.

Noticed a slightly extended crank a day or so ago, along with a few seconds worth of poor idle and then ran as normal.

Checked for codes, and none showing.

Checked plugs when I got home again and all ok.

Checked the lpfp count and was at or around 50% at idle. No hesitation or misfires and none detected on scanner.

Rail holding pressure within parameters and both lpfp and hpfp showing requested and actual pressures where they should be.

Checked the plugs again this morning on a cold engine for damp, and they were dry and showing no signs for concern.

And now for the culprit.

On a stone cold engine, the engine coolant temp sensor was showing 80c while the radiator outlet sensor showed about 1c within ambient air temp.

A new coolant temp sensor now fitted and all showing back within normal tolerance levels and no more extended crank issue.

Just thought this might be useful for anyone with the same problem now or in future and hopefully it saves them time and money.

Good. That you are all sorted. Just out of interest, What is the ambient temperature you are talking about here for Cold Starts? Are you running on E10 or E5 fuel? How old or long / miles have the plugs been in. Did you measure the gap the plugs have when they were out.

Cheers for that @UndertheRadar - good to have it sorted. I guess thinking back to old carb with choke days, it’s running too lean when cold as it thinks the engine is hotter than it is…?

7 hours ago, Evolution13 said:

Good. That you are all sorted. Just out of interest, What is the ambient temperature you are talking about here for Cold Starts? Are you running on E10 or E5 fuel? How old or long / miles have the plugs been in. Did you measure the gap the plugs have when they were out.

Running E5 and mapped for 97ron as that’s the best we can get over here. Literally no where does a 99ron fuel.

Ambient was just literally the outside temp in this case. The coolant at the radiator outlet sensor was reading within 1 degree Celsius of that. Think outside was 16c and outlet reading was 15c.

Main coolant sensor, which in my case on this version of the engine is on the side of the head under the vacuum pump, was reading anything from 78c-81c.

Car had sat all night and hadn’t been started so I could check the readings.

Plugs were changed about 2 weeks ago for another set of genuine OE plugs, which from memory are really just NGK platinum plugs. These get changed every two years and are set to 0.028 and were still perfect when I removed them for inspection.

6 hours ago, travs said:

Cheers for that @UndertheRadar - good to have it sorted. I guess thinking back to old carb with choke days, it’s running too lean when cold as it thinks the engine is hotter than it is…?

Yes, then runs as normal when the engine is warm.

I should have added that the failed sensor also caused oil temp issues, in that it ran the oil temp 20c cooler than it should have been and I noticed it also caused the battery charging state to run low as well.

Great diagnosis, did the dashboard temperature gauge behave normally despite the faulty sensor?

5 hours ago, D402 said:

Great diagnosis, did the dashboard temperature gauge behave normally despite the faulty sensor?

It would show 90c from cold. First day of extended crank I did not notice it as it started and I hadn’t picked up on it. No codes of any description.

Second day from cold I was looking for a fault, so caught temp gauge, but ran through all other scenarios anyway to rule them out.

Had to wait for sensor to arrive as not in stock, so picked up on oil temp and battery charging conditions as I was poking out of interest to see what other areas the sensor effected without alerting most folks to the fact there was actually a fault.

Also no fast idle or warm up sequence as module thought vehicle was already at running temp the entire time.

You would think the system should have a redundancy to verify the coolant sensor, as it does have the use of the radiator outlet temp and oil temp sensors which could be used to determine a fault, but none seem to be built in.

Edited 6 July6 Jul by UndertheRadar