My newly acquired 1978 911SC ran great two days ago when the temperature here in the Boston area was in the 40's. Yesterday, when the temperature dropped to the 20's it ran very poorly - started hard, idled at lower than usual RPM's, and seemed to be misfiring at RPM's lower than 3500 to 4000. Any thoughts on what might be going on?

 

Newly aquired?? Two days ago?

Long term storage and condensation (ICE!)in the gas tank that wasn't nearly full?

 

thanks for responding - I probably didn't give enough detail.
I got the car about a week ago but have not drive daily. I don't think the problem is frozen moisture in the tank because it is in a semi-heated (40 degrees +/-) garage and I've run about ten gallons of gas through the system. I just remembered that I added a bottle of Techron (have used satisfactorily in my BMW) injector cleaner the night before the poor running characteristics. Prior to this week when I got the car it had been stored inside with very little gas in the tank, however, the few times that I test drove it everything seemed OK. I did notice some similar but very slight stumbling on a test drive when put under a load but attributed it to lack of use, old gas, etc.

 

I would drive out most of the gas until about empty. Pour in a bottle of Techron maybe even a bottle and half as the gas tank holds about 24 gallons if I remember right, then fill her up. I would take her out on a 400 - 500 mile cruise to run a complete tank of gas through her loaded with Techron. Keep her at 4000 RPMs or higher on the cruise to really blow out any carbon. At least you will have a blast driving her around..... :-)