I would also like and try to figure out what is causing the rpm gauge to be lower than the engine really is? At idle it reads 400 rpms and while driving it crawls up to about 1500 rpms during shifts when in reality it is about 3k
I had to take out the check engine bulb to pass inspection.
Sometimes, after running a few hours straight, the gauge would go to normal and check engine light would go out. But it has been a few years since it has gone to normal. At one time I was told it read the rpms of the coil packs so I replaced them and still the same. I have also tried a brand new tach and still did the same thing. Could it be the DIS that sends the signal to the tach. I would like to get it tested to make sure it is bad so I don't start throwing parts at this thing. | 
