Every now and then, I have trouble starting it in the morning. The motor cranks, but it does not ignite and start running on its own. It seems to have poor idle. So if I rev the engine once it starts, I can get it to keep running. But if I don't, it will shut down. I had trouble with the same thing a few years ago, but it was fixed temporarily with changing a fuel-mixture sensor. Also, once the engine warms up, it's not a problem. Could it have gone bad this quickly? Would adjusting the idle speed tend to help? Would stepping on the gas while starting tend to help? Thanks.