My 1994 C220 (150k miles) is hard to start and idles rough. If I just turn the key it won't start. If I hold the accelerator partially down, it starts but will cut off unless I let it run for about 5 minutes. It then idles but very rough. However, once I start moving, everthing appears to be ok including the acceleration. I've changed, wires & plugs, checked the gas, and looked for loose connections without success. Any suggestions.