Poor Idle/rough running engine on an 1989 Corvette

I have a 1989 Corvette with 35,000 miles that is having idle and rough running engine problems. The injectors were replaced about two years ago along with the MAF, spark plugs, spark plug wires, distributor cap, and rotor. The engine has ran good until this summer. The problem I have is when the car is first started, it runs very rough and the MPG output on the dash going to 0. Then the engine settles down to an idle rpm of 600 and the MPG output starts to read normally. This has also happen when dirving the car. The engine will run fine while driving, then start to run rough and the MPG will go to 0. After a few miles, the engine will start to run fine and the MPG output will register normal numbers (26-29 miles/gallon). I do not know if I have an injector that is malfunctioning or another problem. Any input would be welcome.

im not entirely sure, but you could have a bad EGR valve, my IROC was doing that for a while, replaced the Valve which had a broken diaphram, and it ran much better.

I had similar problems in a couple of occasions.
One the MAS, air flow sensor, another time were the injectors. A dirty injector(s) will make it run rough. Jose.

You may want to try looking for a vacume leak, I think the mpg gauge works by using vacume somehow and a vacume leak would cause a rough idle concern. What I am not sure of is how you can have an intermitant vacume leak maybe someone here knows of something that may cause a intermitant vacume leak. I know my 92 had a vacume leak near the battery due to acid leaking on the line.

i have the same problem :(