[Eturbo924]

Ok need some help guys.

I just purchased a 1987 928S4 automatic.
I picked it up in NC and drove it home. It performed very well for the first 500 miles or so. Then it started to heat up under the car where I figured the Cats should be. (turns out there are none on my car) The area below the shift lever. It was so hot I could not stand driving with out the window at least partly open. I did look under the car and did not see anything.

Anyway... about 600 or so miles into the 875 mile trip the car would not idle well when shifted into gear. It kind of chugs... or surges. Sounds like it is missing a beat or two. If you shift it into neutral it smoothes out a bit but still not perfect. If you open the throttle a bit it seems to be ok... and while you drive it is ok as well.

So... when I got home I suspected maybe an ignition wire was shorting out. I traced them all and did find one and it might have blown the crap out of the corner of the left bank valve cover with arking or the cover was damaged by the PO. Did not see this of course on initial inspection because you had to take off the air intake tube and move the wire to see it. So that is potential issue.

Here are other thoughts.
Bad O2 sensor? The one in the car looks relatively new but I have no records of it having been changed. Though... most of the exhaust looks new and so does the O2... but that excessive heat could have killed it?

Next... that hole in the valve cover... while needing a repair (or replacement) could it cause the surging?

The last thing. The voltage never seems to be right (battery). It was always around 12 volts when running and seems to fall just below it some times. When the car is doing the surging it jumps between 10 and 12. Only once did I see it at 14.

Help?

Oh all belts were done at 98K miles it now has 115K. Looks like new alternator.