1995 Subaru Outback 95 outback stalls and dies at low speed

I recently purchased a 95 outback it stalls and dies at low speeds and stops but will usually continue to run if you rev the engine in neutral it put out codes 105 106 so I replaced the mass ait, and map sensor and check for vacuum leaks. Since then i have done a fuel injector cleaner, fuel filter and taken it to the dealership and they say nothing is wrong???? When you start it, it runs great and then smokes for aminute or two from under the engine from what I think may be the exhaust??? im not sure, but then it stops and the enigine seems to run fine untill stops ot low speed but the problem isnt constant its everyother stop or so and it happens at odd times not when I first start or after ive been driving for a while but at different times. PLEASE help me....