I have a '79 450 SL with about 140K on it. It's been well maintained and recently been tuned and a new timing chain. It has developed a really rough idle, but it's not consistent. Sometimes it runs well, but most of the time it's very rough. Gets a little better at normal op temp. Basically, it idles so rough it feels as if it will stall. When I hit the gas to accellerate, it runs great. In neutral it idles great. Problem seems to be at idle under the load of being in gear. Once it's warmed up it's better, but not perfect. Seems to miss eratically at idle, but again, once I accellerate it seems to drive well. Any ideas. Help and thanks.