I had the same problem on my one last year. Everything checked out. Turned out it was a bad battery cable. Looked good and new on the outside, but the cables on the inside were done. They can check them for continuity at a shop.
Good luck to you.

 

Well....

Trouble is SOLVED Woooohoooo... Yesterday, I went to two different place with my alternator (remember I sent it to a shop earlier and he told me it was ok). First shop of yesterday told me my amp is working real good. the guy put the alternator on a bench in front of me, ran it a 900rpm and it was reading a solid 13.9 amp. He then put a load of 125amp on it and it read 13.1v. Kinda convincing my self the alt is indeed Ok. I went to a third one and the funny old man told me that my clutch pulley was dead and that he can changed it for a fixed one (no clutch). I argued with him that Porsche wouldn't do that for nothing, he said in french "call your porsche dealer and ask them what was in the 911 in the previous era, that it was a fixed one bla bla bla"... He said he does that all the time on chryslers, hondas and ford .... lol ... neways, he insisted so much that I was kinda scared at the end...

Finally, once the elimination process done (batt good, wiring like new, pulley and belts all good, no ground short... etc etc), I ended u ordering a NEW alternator for only 340$ CAD (quite cheap). It was Bosch made, 100% rebulited by bosch with official logo and warranty. Once installed, I fired up the car and VOILA !!!!!! Solid 14V and idle, Solid 13.8V when all electronics are on and good 13.5V when operating the convertible top... No drop even after 1hrs drive...

I made some calls and was told that once the alt heat up, it can have internal dilatation of its electronic component wich may results in internal failure, short, open circuit etc... Seems like it was my case...

Well, hope it helps you Sunny...

Thanks to all who tried to help.
Bo

 

Well done MZ3BO,

That's good news and on the strength of that and because I was almost convinced about the alternator ( it was just the heating up,thing than threw me) I am going to get a new one.
Brill and thanks for the posting. I'm sure many others like my self will love to know of this sort of problem.

Is there any where on 6speed that archives posts like this for future ref' because it should be stored. You know what posts are like in 12 months somebody else is going to ask all the same questions we have.
Frank
Big thumbs up

 

Ever figure this out?

 

Replaced alternator and exact symptom. Hours and dollars wasted

 

Do you have an aftermarket stereo system (amplifier, sub...)?
It might have to do with the A/C compressor as well if it's not the alternator or the battery.

 

What symptom? Can you describe your case a little more? How many volts are you reading?