I purchased a 1987 s4 in January of this year with 76,000 miles. The timing belt was changed at 62,000 miles and when I had the car checked by a Porsche dealer they indicated the belt tention was fine. Here is the problem. If I start the car, drive somewhat "normal" for 5 min and than start "punching" it the belt tention light never comes on. If I start the car and do not let the car warm up, then punch it, the belt tention light comes on. I have 78,000 miles on the car now and since I normally let the car warm up I have only seen this problem 3 or 4 times. Is the belt loose or are there any other things that could contribute to this situation.?

 

So this guy goes to the doctor and says, "hey doc, when I bend my arm like this it hurts!" so the doc says, "don't bend your arm like that"

Let the car warm up. Your tension is probably on the light side. It's not a big deal to adjust it. What you're probably seeing is that the 928 has an automatic tenisoner based on engine heat. as soon as engine oil heats the bi-metallic discs in the tensioner, they add some tension to the belt. "punching it" tightens the belt on the tight side but puts slack in the slack side where the sensor is.

Sounds like the adjustment is just on the border...

 

I think the explanation is off 180 degrees. As the engin warms up, the block expandes. This increases the tension on the belt. The bi-metallic washers in the tensioner actually work to release tension on the belt through out this process.

I experienced similar tension alarm feedback. The problem was much more extensive than a lighter than average tension setting. Two things to inspect immediately: The belt tension and its condition, and the condition of the tensioner and especially the rubber boot around the tensioner. If the tensioner does not hold oil, it does not function properly.

Take this issue very seriously, as timing belt failure will do big dollar damage to your shark.