I found a similar post from a year ago, but no one ever offered a solution. 83 22r, when the weather is cool (which doesn't happen often here in Ft Lauderdale) the tach acts odd. It will either stick at some number, like 2000 no matter if I'm sitting at idle or running 45MPH in 3rd gear, or sometimes it will sit at 0 (this is usually for a few minutes right after startup). By cool weather, I mean high 50s or low 60s, so not particularly cold for you northerners, but enough diff from the normal high 80s. When the ambient temp rises, the tach acts perfectly normal.