I have 99 Galant 2.4L dohc. It recently started idling and runningvery rough with the engine cold. As soon as the engine reaches operating temp it smooths out and runs great. Took it to Auto Zone and the only code that came up was cylinder 1 misfire. I have replaced plugs and wires. Didn't help. Any ideas for a newbie.

Also was wondering it has 140,000 miles on it. Don't know when or if the timing belt was changed, would this be a wise investment and how expensive of a job is this.

Thanks in advance.

 

1. A US 99 with a 2.4L is a SOHC.
2. The timing belt should be changed every 60,000.