Poor starting when cold
On cold mornings my 2006 Renault Megane 1.6 petrol cranks for a long time and doesn’t fire easily. The battery is quite new, so the engine spins and spins quickly on the starter and will cough and splutter into life if I press the accelerator pedal while cranking – you have to operate the brake pedal while pressing the engine start button on this model. At warmer temperatures, the engine starts up OK but doesn’t settle into a nice idle until I’ve revved the engine a couple of times. For the first mile or so of driving, the engine feels very flat without any power, but after this time the engine runs and drives fine. There is quite a strong smell of petrol and white vapours from the exhaust when it does eventually fire from cold.
My initial thoughts were a problem with the coolant temperature sensor or the air temperature sensor, but I checked both at a cold start and the readings were accurate. I used the live data on my Foxwell NT614 and the CTS was 8°C and the IAT was 4°C, so the car knew it was cold. I watched the CTS readings go up as the engine warmed and the readings were plausible. I can only find one CTS on this engine and it has two wires – is it shared with the dashboard temperature gauge? John Hardy
There is only the one CTS, and as you have checked the reading with both the coolant and air temperature sensors these can hopefully be discounted. As the engine does emit some petrol vapour when starting, it would also appear that the injection system is working, along with the cold start system. The petrol vapours would suggest that the engine may be flooding, which suggests a lack of ignition. This may be for a couple of reasons and the first simple check I would make is that the spark plugs are in good condition. After confirming that the plugs are not the problem, then the trouble could be with the crankshaft sensor. This sensor is a common failure point and is affected by temperature. I have even heard of mechanics using a hair dryer to warm up the crankshaft sensor before starting the engine!
Finally, there were a couple of different versions of the 1.6 engine and you have not mentioned if yours has variable valve timing. If it does then you may be suffering from a dephaser pulley problem. The dephaser pulley normally emits a knocking noise at start-up if it is failing, but this may not be the case.