Porsche Repair: 99 boxster, fuel injection computer, radiator fluid

Question
I have a 99 boxster with 35000 mile on it. Often the engine will die on me after getting off from main highway and come to an complete stop at the traffic light. It seems to be fine when I drive locally but once driving on a highway with higher speed, the engine will die on a complete stop. but it will restart fine.

I checked the oil level and radiator fluid and they are ok.

what could be the problem?

thank you in advance...

-Tony

Answer
Tony,

Just to remind you, my expertise lies in the older 356 models.  Luckily, many early designs/concepts have lasted since the early 50's and appear in revised forms on 911's, 914's 944's, Boxsters, etc.  Where this happens I'll promise to try to give you the best answer I can.

There are a couple avenues to follow in cases like this.  One is tune-up related items like:

1. mis-gapped or old spark plugs
2. dirty or old rotor/distributor cap internals

More likely, the cause is one of these:

1. idle set too low
2. vacuum leak(s)
3. faulty oxygen sensor

If it were me, the idle speed would be where I'd start...the problem for you will likely be that the fuel injection computer probably sets the idle itself.  There may be a way to manually adjust the idle, but I'm just not familiar enough with the Boxster.

I hope these ideas lead you to a quick resolution.

Dave