Porsche Repair: 87 Porsche 928 S4 - Runs Rough When Cold, porsche 928 s4, coolant temperature

Question
I've read a couple of questions on here that are similar to my issue, but don't seem to be exactly the same as mine, so I thought I'd ask for my particular issue:

I've had the 928 running great this summer. It has started and run pretty well in the warm weather. But as the first hint of Fall has arrived and the mornings have gotten a little colder, the 928 idles and runs rough until it warms up. Once warm, the car runs just like in the middle of summer, but until warm, she hesitates and stumbles, especially on accelleration. The only way to prevent this is to keep the throttle really low. When low, the car runs normally, but you can't go very fast! As soon as you apply any pedal, it starts to stutter.

Any ideas?

Thanks,

Marcus

Answer
Hi Marcus,

I'm a bit surprised this condition started when it was cool but not cold weather.  Or...you are just very attuned with your car's performance!

The most likely culprit is your thermo-time sithch which activates the cold start valve.  The switch senses coolant temperature and sends voltage signals to the cold start valve until the coolant passes a "warm" level.  The cold start valve supplies extra (tiny amounts, but extra) fuel to compensate for the cold staring and running needs.

Checks this out first.

Dave