Subaru Forester 1999 light grey/black smoke.

Is check engine light on? If so what are the codes?

http://autorepair.about.com/library/firing_orders/bl-fo-4236.htm --- are you positive the plug wires were installed correctly? Were all the plugs fully installed in the head? The link above shows the proper plug wire locations. Did you use quality plugs? Could any wire harnesses have come loose while changing the plugs? Black smoke normally means un burnt fuel. Double check everything that was done while replacing the plugs also check anything that might have got broke or unplugged while changing the plugs. Also make sure that all wires are fully snapped down on coil and plugs.

This is the image in dandyoun's link...Excellent answer ....just trying to help, I don't know if his device can do it.

Now, about too much oil. If the crankcase is overfull, the crankshaft will dip in to the oil and whip it in to a foam, like a cake mixer. That will play havoc on all sorts of things. I don't know that you had THAT much over, but if so might be at least part of the problem

Thanks for all of your help i appreciate it. Anything else you could tell me to check for would help alot, thanks Quazi187

Check engine light is not on..

Go have the codes read with an OBDII scanner, that'll tell you a lot, were the plugs you bought pregapped spcifically for the car or were they plugs that you needed to gap yourself?

Quazi187, is that a turbocharged 2.0 Forester? Those aren't in the US, so our advice on OBDII codes likely won't help you. Where are you located?

Im from New Zealand, just gonna take it in to amechanic & get it looked at. Thanks for your help guys