With the car injected and converted to mass air did they do the mass air conversion properly? These are the instructions for the Pro-M mass air conversion:
What is missing from the instructions above is as follows:
In 1986-88 vehicles, you may need to connect other wires to avoid EEC error codes. These are:
Pin 19 is the fuel pump monitor. A wire with a pin is provided to put in pin 19, and it must run to the got wire on the fuel pump. Pink under driver seat Pk/Blk. This wire is only necessary if you do not want a diagnostic code. Omitting this wire will not help performance.
Pins 3 and 6 are vehicle speed sensor lines, and will affect some closed throttle operation of your car. Pin 6 is the Orange (-) wire and should be spliced/soldered to the O/Y (-) wire of the speed sensor. Pin 3 is the Green (+) wire and should be spliced/soldered to the DG/W (+) wire of the speed sensor. These wires are found in the driver side kick panel or at the tail shaft of the transmission where the speedo cable connects to the VSS sensor in the transmission.
First thing is check for any codes then double check the mass air conversion. From there probably a base idle reset and possibly a tune up (plugs, wires, cap, rotor, etc.). Simple free stuff first.