I have an 87 Turbo Buick Skyhawk.....the problem I have is that the tac needle is erratically hunting as much as 2K RPMs. With the engine running, I did get several 'check engine' lights and then they went away. Then the tac needle started to hunt erratically, but no more check engine lights came on. I disconnected the battery to reset the ECU and that did not help, all that did was clear the fault code so I have no idea what sensor is going bad (yeah, I know, I'm a dumba** for doing that). When the car is cold, the tac works fine, but when the engine is up to temp, then the hunting starts, so my guess is that heat is causing a sensor malfunction, BUT WHICH ONE(s)????? anyone have similar problem? your solution(s)? your assistance is appreciated!

Update: Parts people think that it is a short somewhere, but I am not convinced as the car runs great when cold and needle doesn't hunt any, the tac only acts-up when hot. Plus I drove it 300-miles at a slower speed (62-mph) and it did not miss a beat. Will update as I get more info, anyone have any ideas?

OK so I found the cause of the tach needle hunting, it was a bad spark plug wire! hope this helps someone in the future!