1990 Saab 900 performance problem

Black smoke means the vehicle is running really rich , do you know what that means ? lacks power when accelerating could be plugged catalytic converter . Fouled spark plugs . Leaking , fuel injectors , fuel pressure regulator leaking .Air filter clogged .Hooking up a scan tool an checking fuel trims , seeing if the computer is taking fuel away or adding .Seeing what the computer is seeing
Why black smoke coming from my car engine Troubleshooting 1 Must Watch

black smoke indication of running rich

turbo probably siezed on it , may need to get a replacement or rebuild , it may also be a vacum problem check the vacum hoses to the turbo and the waste gate

Suspect cracked injector(s). I drove a truck with cracked injector and it billowed black smoke. Power loss can be anything from a sensor to a clogged filter. try changing the fuel filter.

so P, N, and R work just not drive right?

could be EGR, Idle air control valve, is it running rough when driving or is there any white smoke out the tailpipe

The valve stem oil seals require replacement.
This repair can usually be performed without removing the head from the engine, so it should not cost too much.

it all depends on what color the smoke is. if it is black then that means that the engine is burning oil. if it is white then that means that is burning coolant. if it is burning oil then it needs new piston rings. if it is burning coolant then it can either be a blown head gasket or it is leaking through a coolant passageway in the engine itself and would need a new or rebuilt unit.

Have you taken a spark plug out yet? You may have fowled them out. if they are not clean and have a whitish tone to them, then they need to be replaced.

One way to check for a blown head gasket, is to simply smell the coolant reservoir. Pop the cap, and see if it smells like raw gas. Every headgasket, I've diagnosed has had this smell, even if the oil is not contaminated. Another way is to hook up a coolant pressure tester, and run the vehicle for 15-20 mins or so. If the head gasket is blown, the pressure will exceed 15 psi. sometimes as high as 25 psi. If there is oil in the coolant overflow tank, the head is cracked, about 90% of the time.
I'm working on a 03 Saab 95 2.3l t. This vehicle smokes on initial start up, then the smoke disapates, and the vehicle is fine. Another mechanic diagnosed it as bad valve seals. I disconnected the pcv system, and the vehicle no longer smokes. If the valve seals have gone bad, the vehicle will smoke on acceleration. Also if the turbo seals are leaking it will smoke more heavily on acceleration.