Saxo SX 1.4 petrol automatic stalls after cold start

[Uriil]

i only own it for few weeks, that issue happened first on April 1. Recently i changed coolant after it shown me overheating warning light (i stopped for 10 minutes with opened bonnet then arrived home where saw light again). max 5 seconds before i switched engine after light appeared. (2 000rpm - max)
Issue itself: in the morning (15 hours since engine was stopped) i started engine 4-5 times but every time it choked and stalled. Then i decided to help with accelerator and it worked, after 1 minute it didn't need help and worked fine on idle. I decided to risk and drove to work (only 4miles away). Since that i probably done 18 miles, apart of problem with start(i now always help with accelerator) car works fine: no stalling during driving, no sudden rpm increases or decreases.

Gemini suggested that green temperature coolant sensor can be a cause of the issue because ECU doesn't understand that it's cold start (logically could be damaged during overheating). It offered to disconnect sensor and try to start without (ECU should according to Gemini start to work in cold start mode), i did it but it was exactly the same.

Did anyone else had similar issue? What to check next? i have no scanner to do diagnostics. Thanks in advance

[PaulC5]

What year is your car ? If an early C3 there will be 2 temperature sensors, a green one and a bit lower a blue one. Both of these can give a false high temperature warning so you could do with replacing them. Since you have found disconnecting the green one made no difference try disconnecting the blue one. There was recent similar topic and it was the blue one that was faulty. viewtopic.php?t=89004

If your gemini garage is not helping much you are better to ask real people as on this forum. Somebody else was using chatgpt (?) for advice and seemed to be getting duff answers.

[Uriil]

What year is your car ? If an early C3 there will be 2 temperature sensors, a green one and a bit lower a blue one. Both of these can give a false high temperature warning so you could do with replacing them. Since you have found disconnecting the green one made no difference try disconnecting the blue one. There was recent similar topic and it was the blue one that was faulty. viewtopic.php?t=89004

If your gemini garage is not helping much you are better to ask real people as on this forum. Somebody else was using chatgpt (?) for advice and seemed to be getting duff answers.

it's Saxo 1.4 2000. will try to disconnect blue one, it's easy. But as far as i understand, blue one is responsible for dashboard indication mainly. Will update on results

[ozvtr]

So the engine will start if you give it some accelerator? But then dies when you release the throttle? However runs fine when warmed up?
Any other symptoms? Loosing coolant? Engine oil changed colour or viscosity?
Checked vacuum line to brake booster?

[ozvtr]

Recently i changed coolant after it shown me overheating warning light

Do you know if the radiator fans came on at the same time?

[Uriil]

Recently i changed coolant after it shown me overheating warning light

Do you know if the radiator fans came on at the same time?

no, radiator didn't work at that time. turns out coolant level was too low or air stuck in radiator or all together. When i changed it - only 2L drained via bottom hose connected to radiator

[Uriil]

So the engine will start if you give it some accelerator? But then dies when you release the throttle? However runs fine when warmed up?
Any other symptoms? Loosing coolant? Engine oil changed colour or viscosity?
Checked vacuum line to brake booster?

yes, accelerator is required for about 20 second - after that it run on idle well. So far no other symptoms, yesterday it started ideally without accelerator help, but it was midday. +15C and sun heated bonnet for hours

[PaulC5]

If not done already, clean in the throttle plate area to remove any carbon build up. You can use a carburettor cleaner spray or a cloth damp with turps/white spirit.

[Uriil]

Issue disappeared itself. after few weeks issue disappeared, nothing was done with a car

[ozvtr]

It's possible the problem was the green temp sensor. The engine ECU uses the coolant temp to initially set the air/fuel mixture. The engine ECU uses two temp sensors to determine the air/fuel mixture, the other is in the Manifold Absolute Pressure (MAP) sensor. That's plugged into the inlet plenum.
Forget the "blue" sensor (if the engine has one). That has nothing to do with the fuel mixture. It's only an over temp indicator.
But if the green sensor failing is the case, I'd expect it to fail again. However, those sensors tend to fail outright. They don't tend to "sort-of" work.

Has the engine started working properly since the weather has changed? Is the weather there getting warmer? Would you say it starts better in warmer weather?

[Uriil]

It's possible the problem was the green temp sensor. The engine ECU uses the coolant temp to initially set the air/fuel mixture. The engine ECU uses two temp sensors to determine the air/fuel mixture, the other is in the Manifold Absolute Pressure (MAP) sensor. That's plugged into the inlet plenum.
Forget the "blue" sensor (if the engine has one). That has nothing to do with the fuel mixture. It's only an over temp indicator.
But if the green sensor failing is the case, I'd expect it to fail again. However, those sensors tend to fail outright. They don't tend to "sort-of" work.

Has the engine started working properly since the weather has changed? Is the weather there getting warmer? Would you say it starts better in warmer weather?

now i am almost certain it was coolant leak to one of the cylinder(s). Small amount of coolant collected in the cylinder overnight and it took some time to burn it with fuel at the start. When level of coolant dropped in few weeks, pressure in a cooling system dropped(more space in cooling system for compressible air was now available instead of uncompressible liquid). Issue with cold start disappeared completely, i think because leak of the coolant stopped or became tiny.

old lady is still running, no overheating, but all my rides are very short - 7 + 7 miles max, no real test for her.