I have had this car for 6 years. I am really happy with it. Over the last 40,000 miles it has developed an ignition problem that the main dealer can't solve. During the summer only, when the weather is warm, if the car gets warm in traffic or is left to stand with the engine off after it has been running for some time, it misfires. The way to solve this is to leave the bonnet open (hood if you are in USA) for 2 - 3 minutes. It then totally recovers and all runs normally. If the bonnet is not opened, it will need 30-40 minutes before it will start normally. The fault code says that there is injector failure for cylinder 4. Swapping injector 4 for injector 5 makes no difference - it still registers injector failure cylinder 4. There is really nothing to suggest a problem with the injectors. All the following have been done with no effect; All 5 coils have been renewed. All plugs replaced. Air mass meter replaced. New air filter. When not misfiring the engine runs perfectly. No loss of power or fuel economy. Any ideas please?

 

have dealer checked how ECU is being cooled?