I have a 1988 firebird formula with a TBI 305. went to start it yesterday and the tachometer shot up to 6000 rpm while cranking off the starter. it will read anywhere from 1500-6000 rpm while tryig to start it. it has backfired a few times and is making some not so great sounds. I disconnected the fuel injectors while checking for spark with a timing light and it ran off of the fuel that was already in the intake and seemed to be running fine around 1500 rpm for a few seconds. I have spark and its fairly consistent and seems to be how it should be.

I used the electronic spark timing bypass to see if it would run without the computer trying to adjust the timing, it ran but was chopping and couldnt hold steady rpm, and was sounding really terrible.

When in run with the engine off the tachometer would randomly shoot up to the max it can go, and when it did that the fuel pump started running. I could get the tachometer to move when i put it into gear or put my foot on the brake. Assuming something went wrong electrically but i dont know where to start.

 

Ouch, you have a few gremlins going on at once. Try replacing some fuses in fuse panel under steering wheel. There should be one for gauge cluster. Might be long shot but cheap enough for new fuses to try it out. Check out this youtube video for what each fuses is for on your car. Maybe there is a ground wire somewhere not working properly?

 

Pulled off the ground on the back of the driver side head. Someone did a half *** job at recrimping a ground lug on but i redid that and its driveable now. Tach is still going crazy on startup but as soon as it starts it runs and drives fine. My guess is the next thing to check will be the power going into the fuse block because in run the tach still goes up to 6000 if i put my foot on the brake pedal. thanks for the respose