1985 745t

Drove to Wal-Mart and when I came back out and started the car it began WILDLY fluctuating at idle. Basically the tach jumped to around 1300, then up to around 1900, then bottomed out around 500 or something, then back up between 1300 and 1900, etc. There was no apparent rhyme to the fluctuations, and the movement was VERY fast (faster than it generally changes with use of teh accelerator). Car continued to fluctuate throughout the trip home, mostly when I was either traveling vary slow, had the engine out of gear, or was stopped and idling. Whenever that tach jumps while driving the car bucks somewhat.

As an FYI, Today I gapped and replaced the spark plugs. Regular, standard green bosch plugs that I've used forever (WRD7?). The ones that came out had the proper greyish tan coloring, with no visible damage, wetness, or burning. The new plugs went in without a hitch, and the wire boots are all snug and secure. The only negative was that I found one of the "fins" from the exhaust manifold that the front plug boot sits in (the fin that bends out toward the turbo) had corroded off its two bolts, and I pulled it free lest it cause damage to any other parts when it finally broke free.

So here are some specific questions, though any direct advice is appreciated:

1. Could the lack of that fin cause the boot (its the first/front plug) to heat up enough to cause a problem?

2. Irregardless do I need to worry about a missing heat sink fin (I'm assuming its there to absorb heat that might affect the boot)? The other plug boots seemed just as hot when I checked, but I can't imagine its there for no reason.

3. Is this an AMM problem? It seems like an AMM problem would be more consistent than this, like I would just "have a problem" and not this in and out kinda thing, but I don't know.

4. Is it possible I damaged a plug wire when I removed them? One of them was pretty tight and had to be pulled up, but I was pretty careful and didn't just yank it free with the wire or anything.

Since I've gotten the car back home I have been unable to replicate the problem in the driveway (typical...). I'll post an update if I uncover anything else, but any help is appreciated. FYI, playing with the AMM harness and jostling the AMM while the car is running had no apparent affect.

Thanks in advance.

-rt