General help ?

[ACFD108]

I have an 87 Grand Natioanl with 31,000 Miles this morning it started to spit and sputter and wouldnt go over 25-30 MPH. It also started to blow some light black smoke when under a little load I know the gas it is is new had the fuel injector cleaner added also octane booster All this is what I usually do. Just wondering before
I dig into this

 

[Turbo Brian]

got a scan tool? my first guess is MAF, especially if thats still the original.

 

[Roger]

Lightly tap the MAF with a screwdriver handle while the engine is ideling, any changes will point to a bad MAF.