92 SHO mtx engine problem - HELP!

[firefly4]

I have a bad problem. I'm in love with this car and need it to be fixed, so I'll my best to detail the problem. Any help is greatly appreciated.

SYMPTOMS:

-Power loss
-Check engine light comes on
-tachometer will not report true engine speed (I know this because when driving down the highway at 50 mph, I do not lose any speed, yet the tach will drop)
-also the tach is sometimes very "bouncy"
-very rough drive
-feels like it's missing 2 to 4 cylinders at times

WHEN IT HAPPENS:

-cold/hot/idle, driving, stationary, in gear out of gear makes no difference

PERSISTENCE:

-not persistent problem, it comes and goes
-there is not way for me to tell if it will run well or not
-I can tell when it is about to run well though, say it's running bad, then all of a sudden the tach will jump up to the true engine rpm, and the check engine light goes off, all I have to do is wait 3-4 seconds then, wham! all cylinders kick back in and drive okay for a while

FIRST TIME IT OCCURED:

-On a very VERY cold day (In in Canada) about a month ago, I started the car, must of had a weak coolant mix, cause the water pump blew.
-Antifreeze all inside under hood in car.
-Had to drive it to my garage (ten minutes)
-After having the water pump replaced I have had this problem

MEASURED ALREADY TAKEN:

-Garage suggested putting in 6 new plugs to help create a healthy spark, but I still get exactly the same problems (I do have more power when it works well though, but the intermittent problem is still there)

ERROR CODES:

-211 - Profile Ignition Pickup Erratic
-216 - Coil 2 primary ckt fault
-217 - Coil 3 primary ckt fault

MY HUMBLE OPINION:

Possibility 1
It could be the crank position sensor, since the sensor would have been coated with coolant when the water pump was leaking, and this would explain the erratic ignition error code and jumpy/bad tachometer readings. I'm guessing that the coil errors are a result of the knock sensor blocking those coils from discharging. I don't know if it's possible... but that is my only guess for this scenario.

Possibility 2
Those two coils are failing. That is why I lose 2-4 cylinders at a time. I wonder if this would cause the tachometer reading problems though? Would coolant being spilled under the hood do this, the water pump going is the precursor to all of this remember.

Well, thanks a bunch for reading this, and thanks if you decide to post suggestions. I'm really desperate for opinions at this point.

[Acidbath]

well, from the few strange electrical problems I've personally seen with these cars, they have all resulted in a bad alternator. Dont reallly know why but it has always been. The coils rarley fail, so i dont know what to tell you there. The crank sensor if it acts up shuts the engine down, so I would say check that alternator output and make sure its doing okay, maybe its not sending enough voltage to the coil?! i dunno.. let me know what u find out

[firefly4]

Well, no far I replaced the plugs and crank sensor with no results. I think the next step would be the coils. I'm having a different shop hook their scanner to it to diagnose the problem (they are supposed to be the best in town).

[firefly4]

Turns out it was a faulty ICM. It was killing 2-4 cylinders at random times. Got a new one in and it's working great now!

Thanks for the advice Acidbath.