Ive got a 91 535i that runs very rough when it is started cold in the mornings. i replaced the headgasket on it about 100km ago. I have read up on what could cause this, and one thing is it could be the coolant temp sensor. i just measured it then and it got a reading of 3.57K. this was taken with the motor stone cold (hasnt been started for a few days) and it was only a max of 14degrees celcius today. i do not think it is anything to do with the headgasket, as when i rev it it blows a dask colour smoke (not white steam).if i rev it and keep it at about 1500rpm for about 30secs it will then idle fine. i have had it upto its proper operating temperature and the system was pressurized as normal, i then parked the car and felt the hoses 2 days later and they were still sort of hard so i dont beleive there is a leak of any sort. If anyone could help me it would be appreciated.