I recently bought a '91 Z28 with an L98 350. When I bought the car it had a battery about the size for a Geo. I replaced the battery and the starter (it went out also),the car started ok for a while. I think I may have a bad relay, is there any way this can be checked? Also just so you Know the guy I bought the car from or the guy he bought it from did a real hatchet job on the emission system from the air pump right down to the cats, resulting in a rough idle. The car was purchased through E-Bay, and I got a great deal if I can get it to run correctly. Any help is appreciated.

 

I had this problem also on my '91 L98. Turned out to be a bad TPS (throttle position sensor). Try this link
http://www.thirdgen.org/tpimod2
Now, on your '91, you won't be able to adjust it but you should be able to see where your voltage is. When the gas pedal is pressed all the way to the floor, the computer will kill the injectors, keeping the car from starting. When I checked mine, I had a voltage of 5.4 which was telling the computer that the car was floored, even though it wasn't. This was keeping it from starting. I swapped sensors and it fired right up. As far as the emissions, just make sure all the holes are plugged so you have no exhaust leaks and then set the IAC as shown in the link above. Hopefully that will make you good-to-go. Good luck!