i was gonna say ICM myself. mine did that for like 2 years, then my ICM finally hit a brick wall and died, and when i replaced it ( not inexpensive 180ish bucks ) my tach has worked perfect from then on
WOW....omg that was like not only the wrong thread i posted in, but the wrong board completly....this was to go onto a myspace thing, NOT CALLING YOU A LOSER MUSTANGGRN!!!
happy birthday though :)
if after you do your cat, check your ignition module. it may be a problem, mine went out on my 92, and when it did i could barley make it to 30 it seemed