Missing badly when cold and hot - stumped

Well, the 500 has now got me in a pickle here. A little while ago, the check engine light came on and I would get a miss at idle, hot or cold, sometimes speratic, sometimes bad enough that it felt like a rad cam was in the car. Then, under heavy load acceleration it would miss quite bad and bog down. Sometimes it won't happen, then it will. But I've noticed that it does do it when its cold, and if I've driven the car for say an hour or so. Another interesting thing, is if I take a corner sharp at all at low speeds (foot off gas), it will die immediately. So I replaced the spark plugs with Bosch +4s and did an oil change at the same time (needed one), and that did no good. So, I asked some guys, and they all said, replace the MAF. So, being STRAPPED for cash, I got one from a '95 S500 with 66k miles and put it in. No difference. I checked the service records, and this problem had been "fixed" once before at the dealer. They said it was a broken plug wire which they replaced, and also a faulty engine wiring harness (the big guy). That is of course now out of warranty. The engine wiring harness I'm really unsure of it being replaced though. Says in the notes that the wiring harness needs replacement, but in the bill it shows it was replaced, so I can only assume that the note was before the fact and left in. So what the heck is going on here?