check this out! mac tools has a scan tool for 150 bucks...i forgot the model but i just seen it today. this little thing has global communication technoligy, meaning it can communicate with asian import, domestic cars AND european import cars. the cool thing is, it has a live data feature. we tested it out today when my mac vendor was here. you plug it into the OBD2 port and go to the live data feature and run your car. there is a graph that displaysthe RPMs off the pulses from your dizzy...just like my high dollar scope. this will help you figure out what is causing your tach to malfunction and help you diagnose what is wrong with your tach. hope you find a mac vendor, or buy it online if you can. sorry i forgot the model number but it was the only one priced in that price range that can do all that