I got 86 trans-am with 305 tpi, and after I installed a custom cold air intake it starts hard when cold, has rough idle, and a loud hissing sound from intake. Once the engine warms up it all clear up. I unplugged the maf and it started easier, idle was smooth, and wasn't making the hissing sound. Also in the past month or so I lost 75 miles on a tank of gas. I dont know if the ses light is coming on because it didn't work since I got the car.
Any suggestions?

 

Go back to the stock intake and see if it runs normal again. MAF's are very sensitive to intakes and if the flow isn't right across the metering portion, or the flow is too turbulent, you wind up with lots of strange problems.