There are a lot of threads on here that detail this problem and other possibilities. The coil wouldn't just die because it got wet, but apparently when they do fail its on a partial fail basis. Something to do with the inside of the coil and the way it works - beats me though.

Another thought, check the dist. cap/rotor and the wires and plugs. Again, same thought as the coil, if you haven't replaced them, it might be the problem, might not, but in either case it will only make the car run better.

If you search, there are threads that also reference the temp sensor on the engine (I believe) and the crank position sensor as possible problems, along with vacuum leaks.

There is also the possibility of carbon build up on the back of the valves, in which case you should run some injector cleaner and drive the car harder.

Last but not least, it could be the fuel injectors/fuel injector seals. Apparently if these are bad, the result could be a similar problem to what you describe.

Hope all this helps. Its not as detailed as other posts on here, but it gives you a starting point to search out the more technical answers. Good luck w/ the coil.

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87 300E
202k on the clock