No clue! from road speed if i step on it the engine generates a vibration when under boost, if i just give it enough throttle to aquire 0.0 psi. To equilize boost and vaccum it purrs no problem. also a vibration at idle... New plugs/wires..fresh oil ..air filter 315 000 kms on relitivly well maintained engine. any additional info needed? Possible problems? Things to check over?

I had same problem with my 93 non-sc. I had new plugs and wires too. Turned out to be coil(*). Willwren said this is indicative of ignition... so, per my FSM...
The quick check to find the cylinder is:

Something else that might help find the baddy; when I would pull the wire off a GOOD coil terminal, I would observe lots of arcing from the terminal back to the coil body. On pulling off a wire from a BAD coil, there would be NO arcing. In both cases, the coil would only be bad on one side; the other side worked fine.

Ok THX i will try that. is it also a possability that a coil issue would make it hard to start the car on cold/cooler mornings(sitting over night) but start fine on warm mornings? Also if i shut the car off for say 15-20 min.. when i fire it up again it will idle errattic and stall if i dont give it any gas...ideas?

I would only be guessing at this point, but the cold vs. warm piece would seem more air/fuel related. Also, my SSE is NA, so I'm not comfortable diagnosing SC things. But if you are missing spark, it may be effecting your start up too. A guess.

ya i think maybe it is the FPR for your help. would a faulty coil cause my tach to malfunction?

The tach gets a signal from the ICM. Assuming 98 ICM is the same, the white wire on pin E of the ICM is the tach output. So, another thing would be to unplug and clean the ICM male and female connectors. Something like carb cleaner may do the trick.