[1989Corvette]

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.